6.alpha.-alkyl-6,7-dione steroids as intermediates for the production of steroidal FXR modulators

ABSTRACT

Disclosed herein is a process for the preparation of a compound of formula (I) and related methods. The compounds of formula (I) are intermediates in the synthesis of synthetic bile acids and its analogues, and the compounds of formula (I) have pharmacological activity. Methods include the synthesizing of these intermediates, and methods of preparing obeticholic acid and obeticholic acid analogues from the prepared compounds.

PRIORITY

This application is a divisional application of U.S. patent applicationSer. No. 15/528,341, filed May 19, 2017, and which was abandoned. U.S.patent application Ser. No. 15/528,341 claims the benefit ofInternational Application No. PCT/GB2015/053519, filed Nov. 19, 2015,which claims the benefit of GB Patent Application No. 1420593.4, filedNov. 19, 2014, GB Patent Application No. 1420594.2, filed Nov. 19, 2014,and GB Patent Application No. 1505675.7, filed Apr. 1, 2015, thecontents of which are hereby incorporated by reference herein in theirentireties.

The present invention relates to compounds which are intermediates inthe synthesis of bile acid derivatives with pharmacological activity. Inparticular, the invention relates to intermediates in the synthesis ofobeticholic acid and its analogues. In addition, the invention relatesto a method of synthesizing these intermediates and a method ofpreparing obeticholic acid and obeticholic acid analogues from thecompounds of the invention.

Bile acids are steroid acids which are found in the bile of mammals andinclude compounds such as cholic acid, chenodeoxycholic acid,lithocholic acid and deoxycholic acid, all of which are found in humans.Many bile acids are natural ligands of the farnesoid X receptor (FXR)which is expressed in the liver and intestine of mammals, includinghumans.

Bile acids are derivatives of steroid and are numbered in the same way.The following shows the general numbering system for steroids and thenumbering of the carbon atoms in chenodeoxycholic acid.

Agonists of FXR have been found to be of use in the treatment ofcholestatic liver disorders including primary biliary cirrhosis andnon-alcoholic steatohepatitis (see review by Jonker et al, in Journal ofSteroid Biochemistry & Molecular Biology, 2012, 130, 147-158).

Ursodeoxycholic acid (UDCA), a bile acid originally isolated from thegall bladder of bears, is currently used in the treatment of cholestaticliver disorders, although it appears to be inactive at the FXR.

As well as their action at the FXR, bile acids and their derivatives arealso modulators of the G protein-coupled receptor TGR5. This is a memberof the rhodopsin-like superfamily of G-protein coupled receptors and hasan important role in the bile acid signalling network, which complementsthe role of the FXR.

Because of the importance of FXR and TGR5 agonists in the treatment ofcholestatic liver disorders, efforts have been made to develop newcompounds which have agonist activity at these receptors. Oneparticularly active compound is obeticholic acid, which is a potentagonist of both FXR and TGR5. Obeticholic acid is described in WO02/072598 and EP1568706, both of which describe a process for thepreparation of obeticholic acid from 7-keto lithocholic acid, which isderived from cholic acid. Further processes for the production ofobeticholic acid and its derivatives are described in WO 2006/122977, US2009/0062256 and WO 2013/192097 and all of these processes also startfrom 7-keto lithocholic acid.

It is clear from the number of patent publications directed to processesfor the production of obeticholic acid that it is by no means simple tosynthesise this compound and indeed the process which is currently usedstarts from cholic acid and has 12 steps and an overall yield of only5-10%.

In addition to the inefficiency and high cost of this process, there arealso problems with the cost and availability of the starting materials.Cholic acid, the current starting material for the production ofobeticholic acid, is a natural bile acid which is usually obtained fromthe slaughter of cows and other animals. This means that theavailability of cholic acid and other bile acids is limited by thenumber of cattle available for slaughter and, moreover, the price ofbile acids is extremely high. Since the incidence of cholestatic liverdisease is increasing worldwide, the demand for synthetic bile acidssuch as obeticholic acid is also likely to increase and it is doubtfulwhether the supply of naturally derived bile acids will continue to besufficient to meet demand.

Furthermore, the use of a starting material derived from animals meansthat there is the possibility of the contamination of the material whichinfectious agents such as viruses, which can not only be hazardous toworkers but could potentially contaminate the end products if steps arenot taken to prevent this.

Although some patients with cholestatic liver disease can be treatedwith ursodeoxycholic acid, this is also a natural bile acid and facesthe same problems of limited availability and high cost.

In an attempt to solve the problems associated with the use of bileacids as starting materials, the present inventors have devised aprocess for the synthesis of synthetic bile acid derivatives such asobeticholic acid which uses plant sterols as starting materials.

Plant sterols are widely available at significantly lower cost than bileacids and, indeed, are often waste products of other processes. Theinventors have developed a process for the preparation of synthetic bileacids starting from bis-norcholenol (also known as20-hydroxymethylpregn-4-en-3-one), which proceeds via novelintermediates.

Therefore, in the present invention there is provided a compound ofgeneral formula (I):

wherein:

R¹ is C₁₋₄ alkyl optionally substituted with one or more substituentsselected from halo, OR⁶ or NR⁶R⁷;

-   -   where each of R⁶ and R⁷ is independently selected from H or C₁₋₄        alkyl;

R² is H, halo or OH or a protected OH, which is stable under basicconditions;

Y¹ is a bond or an alkylene linker group having from 1 to 20 carbonatoms and optionally substituted with one or more groups R³;

each R³ is independently halo, OR⁸ or NR⁸R⁹;

-   -   where each of R⁸ and R⁹ is independently selected from H or C₁₋₄        alkyl;

and

R⁴ is C(O)OR¹⁰, OC(O)R¹⁰, C(O)NR¹⁰R¹¹, OR¹⁰, OSi(R¹³)₃, S(O)R¹⁰, SO₂R¹⁰,OSO₂R¹⁰, SO₃R¹⁰, or OSO₃R¹⁰;

-   -   where each R¹⁰ and R¹¹ is independently:    -   a. hydrogen or    -   b. C₁₋₂₀ alkyl, C₂₋₂₀ alkenyl, C₂₋₂₀ alkynyl, —O—C₁₋₂₀ alkyl,        —O—C₂₋₂₀ alkenyl or —O—C₂₋₂₀ alkynyl, any of which is optionally        substituted with one or more substituents selected from halo,        NO₂, CN, OR¹⁹, SR¹⁹, SO₂R¹⁹, SO₃R¹⁹ or N(R¹⁹)₂, or a 6- to        14-membered aryl or 5 to 14-membered heteroaryl group, either of        which is optionally substituted with C₁₋₆ alkyl, C₁₋₆ haloalkyl,        halo, NO₂, CN, OR¹⁹, SR¹⁹, SO₂R¹⁹, SO₃R¹⁹ or N(R¹⁹)₂; or    -   c. a 6- to 14-membered aryl or 5 to 14-membered heteroaryl group        optionally substituted with one or more substituents selected        from C₁₋₆ alkyl, C₁₋₆ haloalkyl, halo, NO₂, CN, OR¹⁹, SR¹⁹,        SO₂R¹⁹, SO₃R¹⁹ or N(R¹⁹)₂;    -   d. a polyethylene glycol residue;        -   each R¹⁹ is independently selected from H, C₁₋₆ alkyl, C₁₋₆            haloalkyl, or a 6- to 14-membered aryl or 5 to 14-membered            heteroaryl group optionally substituted with halo, C₁₋₆            alkyl or C₁₋₆ haloalkyl;    -   each R¹³ is independently    -   a. C₁₋₂₀ alkyl, C₂₋₂₀ alkenyl or C₂₋₂₀ alkynyl optionally        substituted with one or more substituents selected from halo,        NO₂, CN, OR¹⁹, SR¹⁹, SO₂R¹⁹, SO₃R¹⁹ or N(R¹⁹)₂, a 6- to        14-membered aryl or 5 to 14-membered heteroaryl group, either of        which is optionally substituted with C₁₋₆ alkyl, C₁₋₆ haloalkyl,        halo, NO₂, CN, OR¹⁹, SO₂R¹⁹, SO₃R¹⁹ or N(R¹⁹)₂; or    -   b. a 6- to 14-membered aryl or 5 to 14-membered heteroaryl group        optionally substituted with one or more substituents selected        from C₁₋₆ alkyl, C₁₋₆ haloalkyl, halo, NO₂, CN, OR¹⁹, SR¹⁹,        SO₂R¹⁹, SO₃R¹⁹ or N(R¹⁹)₂;        -   each R¹⁹ is independently selected from H, C₁₋₆ alkyl or            C₁₋₆ haloalkyl;

R^(5b) is H or OH or a protected OH;

or a salt or an isotopic variant thereof.

Compounds of general formula (I) are intermediates in the synthesis ofpharmaceutically active compounds such as obeticholic acid and itsderivatives.

In the present specification, except where the context requiresotherwise due to express language or necessary implication, the word“comprises”, or variations such as “comprises” or “comprising” is usedin an inclusive sense i.e. to specify the presence of the statedfeatures but not to preclude the presence or addition of furtherfeatures in various embodiments of the invention.

In the present application the term “C₁₋₂₀” alkyl refers to a straightor branched fully saturated hydrocarbon group having from 1 to 20 carbonatoms. The term encompasses methyl, ethyl, n-propyl, isopropyl, n-butyl,isobutyl and t-butyl. Other alkyl groups, for example C₁₋₂₀ alkyl, C₁₋₆alkyl or C₁₋₃ alkyl are as defined above but contain different numbersof carbon atoms.

The term “C₁₋₆ haloalkyl” refers to a straight or branched alkyl groupas defined above having from 1 to 6 carbon atoms and substituted withone or more halo atoms, up to perhalo substitution. Examples includetrifluoromethyl, chloroethyl and 1,1-difluoroethyl.

The term “C₂₋₂₀ alkenyl” refers to a straight or branched hydrocarbongroup having from 2 to 20 carbon atoms and at least one carbon-carbondouble bond. Examples include ethenyl, prop-1-enyl, hex-2-enyl etc.

The term “C₂₋₂₀ alkynyl” refers to a straight or branched hydrocarbongroup having from 2 to 20 carbon atoms and at least one carbon-carbontriple bond. Examples include ethynyl, prop-1-ynyl, hex-2-ynyl etc.

The term “alkylene” refers to a straight or branched fully saturatedhydrocarbon chain. Examples of alkylene groups include —CH₂—, —CH₂CH₂—,CH(CH₃)—CH₂—, CH₂CH(CH₃)—, —CH₂CH₂CH₂—, —CH₂CH(CH₂CH₃)— and—CH₂CH(CH₂CH₃)CH₂—.

The term “alkenylene” refers to a straight or branched hydrocarbon chaincontaining at least one carbon-carbon double bond. Examples ofalkenylene groups include —CH═CH—, —CH═C(CH₃)—, —CH₂CH═CH—, —CH═CHCH₂—,CH₂CH₂CH═CH—, CH₂CH═C(CH₃)— and —CH₂CH═C(CH₂CH₃)—.

The term “alkynylene” refers to a straight or branched hydrocarbon chaincontaining at least one carbon-carbon triple bond. Examples ofalkenylene groups include —C≡C—, —CH₂C≡C—, —C≡C—CH₂—, CH₂CH₂C≡C—,CH₂C≡CCH₂— and —CH₂CH≡C—CH₂CH₂—.

The terms “aryl” and “aromatic” refer to a cyclic group with aromaticcharacter having from 6 to 14 ring carbon atoms (unless otherwisespecified) and containing up to three rings. Where an aryl groupcontains more than one ring, not all rings must be aromatic incharacter. Examples include phenyl, naphthyl and anthracenyl as well aspartially saturated systems such as tetrahydronaphthyl, indanyl andindenyl.

The terms “heteroaryl” and “heteroaromatic” refer to a cyclic group witharomatic character having from 5 to 14 ring atoms (unless otherwisespecified), at least one of which is a heteroatom selected from N, O andS, and containing up to three rings. Where a heteroaryl group containsmore than one ring, not all rings must be aromatic in character.Examples of heteroaryl groups include pyridine, pyrimidine, indole,benzofuran, benzimidazole and indolene.

The term “halogen” refers to fluorine, chlorine, bromine or iodine andthe term “halo” to fluoro, chloro, bromo or iodo groups.

The term “halogen” refers to fluorine, chlorine, bromine or iodine andthe term “halo” to fluoro, chloro, bromo or iodo groups.

The term “protected OH” relates to an OH group protected with anysuitable protecting group. For example, the protected OH may be a groupR⁴ as defined above.

Suitable protecting groups include esters such that, for example when R²and/or R⁵ is a protected OH, R² and/or R⁵ may independently be a groupOC(O)R¹⁴, where R¹⁴ is a group R¹⁰ as defined above. Silyl ethers arealso suitable, and in this case, R² and/or R⁵ may independently be agroup OSi(R¹⁶)₃, where each R¹⁶ is independently a group R¹³ as definedabove.

Other suitable protecting groups for OH are well known to those of skillin the art (see Wuts, P G M and Greene, T W (2006) “Greene's ProtectiveGroups in Organic Synthesis”, 4^(th) Edition, John Wiley & Sons, Inc.,Hoboken, N.J., USA).

References to a protecting group which is stable in basic conditionsmean that the protecting group cannot be removed by treatment with abase.

Appropriate salts of the compounds of general formula (I) include basicaddition salts such as sodium, potassium, calcium, aluminium, zinc,magnesium and other metal salts as well as choline, diethanolamine,ethanolamine, ethyl diamine, meglumine and other well-known basicaddition salts as summarised in Paulekuhn et al., J. Med. Chem. 2007,50, 6665-6672 and/or known to those skilled in the art.

In some suitable compounds of general formula (I):

R¹ is C₁₋₄ alkyl optionally substituted with one or more substituentsselected from halo, OR⁶ or NR⁶R⁷;

-   -   where each of R⁶ and R⁷ is independently selected from H or C₁₋₄        alkyl;

R² is H, halo or OH;

Y¹ is a bond or an alkylene linker group having from 1 to 6 carbon atomsand optionally substituted with one or more group R³;

each R³ is independently halo, OR⁸ or NR⁸R⁹;

-   -   where each of R⁸ and R⁹ is independently selected from H or C₁₋₄        alkyl; and

R⁴ is C(O)¹⁰, C(O)NR¹⁰R¹¹, S(O)R¹⁰, SO₂R¹⁰, OSO₂R¹⁰, SO₃R¹⁰, or OSO₃R¹⁰;

-   -   where each R¹⁰ is hydrogen or C₁₋₆ alkyl or benzyl, either of        which may optionally be substituted with one or more halo        substituents and R¹¹ is hydrogen or C₁₋₆ alkyl, benzyl, —C₁₋₄        alkylene-SO₃H or —C₁₋₄ alkylene-SO₃(C₁₋₄ alkyl), any of which        may optionally be substituted with one or more halo        substituents;

R^(5b) is H or OH;

or a salt thereof.

In suitable compounds of general formula (I), R¹ may be C₁₋₄ alkyloptionally substituted with one or more substituents selected from halo,OR⁶ or NR⁶R⁷, where R⁶ and R⁷ are each independently H, methyl or ethyl,especially H or methyl.

More suitably, R¹ is unsubstituted C₁₋₄ alkyl.

In particularly suitable compounds, R¹ is ethyl.

In some compounds of general formula (I), Y¹ is a bond.

Suitably in compounds of general formula (I), Y¹ is an alkylene linkergroup having from 1 to 15 carbon atoms, more suitably 1 to 12, 1 to 10or 1 to 8 carbon atoms and optionally substituted with one or moregroups R³ as defined above. Typically each R³ is independently halo, OR⁸or NR⁸R⁹; where each of R⁸ and R⁹ is independently selected from H,methyl or ethyl, especially H or methyl.

In some suitable compounds, Y¹ is an unsubstituted alkylene linkerhaving from 1 to 15 carbon atoms, more suitably 1 to 12, 1 to 10 or 1 to8 carbon atoms.

In some suitable compounds of general formula (I), R² is H.

In other suitable compounds of general formula (I), R² is OH.

In still other suitable compounds of general formula (I), R² is aprotected OH group. When R² is a protected OH group, it is a group whichis stable in a basic environment Examples of such groups includeOSi(R¹⁶)₃, where each R¹⁶ is independently a group R¹³ as defined above.

In the compounds of general formula R⁴ is C(O)OR¹⁰, OC(O)R¹⁰,C(O)NR¹⁰R¹¹, OR¹⁰, OSi(R¹³)₃, S(O)R¹⁰, SO₂R¹⁰, OSO₂R¹⁰, SO₃R¹⁰, orOSO₃R¹⁰.

Suitably, is C(O)OR¹⁰, OR¹⁰, SO₃R¹⁰, or OSO₃R¹⁰

More suitably, R⁴ is C(O)OR¹⁰, SO₃R¹⁰, or OSO₃R¹⁰

Suitably, each R¹⁰ and R¹¹ is independently:

a. hydrogen or

b. C₁₋₁₀ alkyl, C₂₋₁₀ alkenyl, C₂₋₁₀ alkynyl, alkyl, —O—C₁₋₁₀ alkenyl or—O—C₂₋₁₀ alkynyl, any of which is optionally substituted with one ormore substituents as described above; or

c. a 6- to 10-membered aryl or 5 to 10-membered heteroaryl groupoptionally substituted with one or more substituents as described above.

d. a polyethylene glycol residue.

More suitably, each R¹⁰ and R¹¹ is independently

a. hydrogen or

b. C₁₋₁₀ alkyl, C₂₋₁₀ alkenyl, C₂₋₁₀ alkynyl or —O—C₁₋₁₀ alkyloptionally substituted with one or more substituents as described aboveor

c. a 6- to 10-membered aryl group optionally substituted with one ormore substituents as described above.

Suitably each R¹³ is independently selected from:

a. C₁₋₁₀ alkyl, C₂₋₁₀ alkenyl or C₂₋₁₀ alkynyl optionally substitutedwith one or more substituents as described above; or

b. a 6- to 10-membered aryl or 5 to 10-membered heteroaryl groupoptionally substituted with one or more substituents as described above.

More suitably, each R¹³ is independently selected from:

a. C₁₋₁₀ alkyl, C₂₋₁₀ alkenyl or C₂₋₁₀ alkynyl optionally substitutedwith one or more substituents as described above; or

b. a 6- to 10-membered aryl group optionally substituted with one ormore substituents as described above.

Still more suitably, each R¹³ is independently selected from C₁₋₁₀ alkylor phenyl, either of which is optionally substituted as described above.

Suitable substituents for alkyl, alkenyl, alkynyl, alkoxy, alkenyloxyand alkynyloxy R¹⁰ and R¹¹ groups and alkyl, alkenyl and alkynyl R¹³groups include halo, NO₂, CN, OR¹⁹, SR¹⁹, SO₂R¹⁹, SO₃R¹⁹ or N(R¹⁹)₂, ora 6- to 10-membered aryl or 5 to 14-membered heteroaryl group, either ofwhich is optionally substituted with C₁₋₆ alkyl, C₁₋₆ haloalkyl, halo,NO₂, CN, OR¹⁹, SO₂R¹⁹, SO₃R¹⁹ or N(R¹⁹)₂; where R¹⁹ is as defined above.

More suitable substituents for these R¹⁰, R¹¹ and R¹³ groups includehalo, OR¹⁹, N(R¹⁹)₂ or a 6- to 10-membered aryl group optionallysubstituted as described above, more suitably optionally substitutedwith halo, C₁₋₄ alkyl, C₁₋₄ haloalkyl, —O—C₁₋₄ alkyl, —O—C₁₋₄ haloalkyl,—NH(C₁₋₄ alkyl) or —N(C₁₋₄ alkyl)₂; for example fluoro, chloro, methyl,ethyl, trifluoromethyl, methoxy, ethoxy, trifluoromethoxy, amino, methylamino and dimethylamino.

Suitable substituents for aryl and heteroaryl R¹⁰, R¹¹ and R¹³ groupsinclude C₁₋₆ alkyl, C₁₋₆ haloalkyl, halo, NO₂, CN, OR¹⁹, SR¹⁹ orN(R¹⁹)₂.

More suitable substituents for these R¹⁰, R¹¹ and R¹³ groups includeC₁₋₄ alkyl, C₁₋₄ haloalkyl, halo, OR¹⁹ or N(R¹⁹)₂, in particular, halo,C₁₋₄ alkyl, C₁₋₄ haloalkyl, alkyl, —O—C₁₋₄ haloalkyl, —NH(C₁₋₄ alkyl) or—N(C₁₋₄ alkyl)₂.

Specific examples of substituents for aryl and heteroaryl R¹⁰, R¹¹ andR¹³ groups include fluoro, chloro, methyl, ethyl, trifluoromethyl,methoxy, ethoxy, trifluoromethoxy, amino, methyl amino anddimethylamino.

As set out above, each R¹⁹ is independently selected from H, C₁₋₆ alkyl,C₁₋₆ haloalkyl, or a 6- to 14-membered aryl or 5 to 14-memberedheteroaryl group optionally substituted with one or more halo, C₁₋₆alkyl or C₁₋₆ haloalkyl substituents.

Suitably, R¹⁹ is H, C₁₋₆ alkyl, C₁₋₆ haloalkyl, or a a 6- to 10-memberedaryl or 5 to 10-membered heteroaryl group optionally substituted withone or more halo, C₁₋₄ alkyl or haloalkyl substituents.

More suitably, R¹⁹ is H, C₁₋₆ alkyl, C₁₋₆ haloalkyl or phenyl optionallysubstituted with one or more halo, C₁₋₄ alkyl or C₁₋₄ haloalkylsubstituents.

Specific examples of R¹⁹ include H, methyl, ethyl, trifluoromethyl orphenyl optionally substituted with one or more fluoro, chloro, methyl,ethyl or trifluoromethyl groups.

In some suitable compounds of general formula (I), R^(5b) is H.

In other suitable compounds of general formula (I), R^(5b) is OH.

In still other suitable compounds of general formula (I), R^(5b) is aprotected OH group.

In still other suitable compounds of general formula (I), R^(5b) is aprotected OH group. When R² is a protected OH group, it is a group whichis stable in a basic environment. Examples of such groups includeOSi(R¹⁶R¹⁷R¹⁸), wherein R¹⁶, R¹⁷ and R¹⁹ are each independently asdefined above but are more suitably C₁₋₁₀ alkyl or C₆₋₁₀ aryl.

Suitably in compounds of general formula (I), Y¹ is an alkylene linkergroup having from 1 to 6 carbon atoms and optionally substituted withone or more groups R³. Typically each R³ is independently halo, OR⁸ orNR⁸R⁹; where each of R⁸ and R⁹ is independently selected from H, methylor ethyl, especially H or methyl.

In some suitable compounds of general formula (I), independently or inany combination:

Y¹ is a bond or an alkylene group having 1 to 3 carbon atoms and isoptionally substituted with one or two R³ groups;

R⁴ is C(O)OR¹⁰, SO₃R¹⁰, or OSO₃R¹⁰, where R¹⁰ is as defined above but ismore suitably H, C₁₋₆ alkyl or benzyl;

R^(5b) is H or OH.

In some more suitable compounds, independently or in any combination:

R¹ is ethyl; and/or

R² is H; and/or

Y¹ is a bond, —CH₂— or —CH₂CH₂—; and/or

R⁴ is C(O)OR¹⁰, where R¹⁰ is H, C₁₋₆ alkyl or benzyl; and/or

R^(5b) is H.

In some particularly suitable compounds of this type, R¹ is ethyl and/orR¹⁰ is C₁₋₆ alkyl or benzyl.

A particularly suitable compounds of the present invention is

(6α, 5β)-3,7-dioxo-6-ethyl-cholan-24-oic acid and C₁₋₆ alkyl and benzylesters thereof and salts thereof, especially the methyl and ethylesters.

Compounds of general formula (I) may be prepared from compounds ofgeneral formula (II):

wherein Y¹, R¹, R² and R⁴ are as defined for general formula (I) and R⁵is H or OH or a protected OH;

by epimerisation.

In some suitable compounds of general formula (II), R⁵ is H.

In other suitable compounds of general formula (II), R⁵ is OH.

In still other suitable compounds of general formula (II), R⁵ is aprotected OH group.

In still other suitable compounds of general formula (I), R⁵ is aprotected OH group. When R⁵ is a protected OH group, it may be a groupwhich is not stable in a basic environment such that treatment with abase converts the protected OH group to OH.

Examples of such groups are well known in the art and include a groupOC(O)R¹⁴ as defined above in which R¹⁴ is a group R¹⁰ as defined abovefor general formula (I).

Particularly suitable R¹⁴ groups are as defined for R¹⁰ above.

Alternatively, R⁵ may be a protected OH group which is stable in a basicenvironment. Examples of such groups include OSi(R¹⁶)₃, where each R¹⁶is independently a group R¹³ as defined above.

The epimerisation reaction suitably comprises treating the compound ofgeneral formula (II) with a base. The compound of general formula (II)may be dissolved in an alcoholic solvent, optionally mixed with waterand contacted with a base, for example sodium or potassium hydroxide ora sodium or potassium alkoxide, typically an ethoxide.

In the case of compounds of general formula (II) in which R⁴ isC(O)OR¹⁰, where R¹⁰ is C₁₋₆ alkyl or benzyl and where a strong base suchas sodium or potassium hydroxide is used, the epimerisation reaction maybe accompanied by hydrolysis to give a compound of general formula (I)in which R⁴ is C(O)OH.

If, in the compound of general formula (II), R² and/or R⁵ is a protectedOH, for example a group OC(O)OR¹⁴, where R¹⁴ is as defined above but isespecially C₁₋₆ alkyl or benzyl, this will be removed during theepimerisation reaction to give a compound of general formula (XXI) inwhich R² and/or R^(5b) is OH. Other protected OH groups which are stablein basic conditions (for example a group OSi(R¹⁶)₃ where each R¹⁶ isindependently as defined above but is especially C₁₋₆ alkyl or phenyl)may be removed subsequently to give a compound of general formula (I) inwhich R^(5b) is OH.

The method is particularly suitable for the preparation of compounds ofgeneral formula (I) in which R⁴ is C(O)OR¹⁰ from compounds of generalformula (II) where R⁴ is also C(O)OR¹⁰, where R¹⁰ is as defined abovebut is especially H, C₁₋₆ alkyl or benzyl.

Alternatively, compounds of formula (I) can be prepared from othercompounds of general formula (I). For example, a compound of generalformula (I) in which R⁴ is C(O)OR¹⁰ may be converted to a compound ofgeneral formula (I) in which R⁴ is C(O)NR¹⁰R¹¹, S(O)R¹⁰, SO₂R¹⁰,OSO₂R¹⁰, SO₃R¹⁰, or OSO₃R¹⁰.

Compounds of general formula (I) in which R⁴ is SO₃R¹⁰ may besynthesised from compounds of general formula (I) in which R⁴ is C(O)OHby the methods taught in WO2008/002573, WO2010/014836 and WO2014/066819.

Thus a compound of formula (I) in which R⁴ is C(O)OH may be reacted witha C₁₋₆ alkanoyl or benzoyl chloride or with a C₁₋₆ alkanoic anhydride toprotect the OH groups. The protected compound may then be reacted with areducing agent such as a hydride, suitably lithium aluminium hydride orsodium borohydride in order to reduce the carboxylic acid group to OH.The alcohol group may be replaced by a halogen, for example bromine oriodine, using the triphenyl phosphine/imidazole/halogen method describedby Classon et al, J. Org. Chem., 1988, 53, 6126-6130. The halogenatedcompound may then be reacted with sodium sulphite in an alcoholicsolvent to give a compound with a SO₃ ⁻Na⁺ substituent.

A compound of general formula (I) in which R⁴ is OSO₃R¹⁰ can be obtainedby reacting the alcohol obtained from reducing the protected carboxylicacid as described above with chlorosulfuric acid in the presence of abase such as triethylamine to yield the protected triethylammonium salt.Protecting groups can be removed using base hydrolysis as describedabove. Reduction of the carboxylic acid followed by reaction of theresultant alcohol with chlorosulfurous acid yields a compound of generalformula (I) in which R⁴ is OSO₂R¹⁰.

Compounds of general formula (I) in which R⁴ is C(O)NR¹⁰R¹¹ may beprepared from the carboxylic acid by reaction with an amine of formulaH—NR¹⁰R¹¹ in a suitable solvent with heating. Compounds of generalformula (I) in which R⁴ is C(O)NR¹⁰R¹¹ or OSO₃R¹⁰ may also be preparedby methods similar to those described by Festa et al, J. Med. Chem.,2014, 57, 8477-8495.

Compounds of general formula (I) with other R⁴ groups may be preparedfrom the above compounds of general formula (I) by methods which arefamiliar to those of skill in the art. These methods also form an aspectof the invention.

A compound of general formula (II) can be prepared by oxidising acompound of general formula (III):

wherein Y¹ R¹, R² and R⁴ are as defined for general formula (I) and R⁵is as defined for general formula (II).

The oxidation reaction may be carried out using any suitable method. Onesuitable method is a Dess-Martin periodinane(1,1,1-triacetoxy-1,1-dihydro-1,2-benziodoxol) oxidation, which may becarried out in a chlorinated solvent such as chloroform ordichloromethane at a temperature of about 15 to 25° C., suitably at roomtemperature.

An alternative oxidation method is oxidation using a hypochlorite, forexample sodium hypochlorite, under acidic conditions, for exampleprovided by acetic acid. The reaction may be carried out in an aqueoussolvent and at a temperature of 0 to 15° C., more usually at about 0 to10° C.

Other oxidation methods include a Jones reaction using sodium dichromateor, more usually, chromic trioxide in dilute sulfuric acid. This processis known to be reliable for the clean conversion of bile acid hydroxylgroups to the corresponding keto derivatives (Bortolini et al, J. Org.Chem., 2002, 67, 5802). Alternatively oxidation may be carried out usingTEMPO ((2,2,6,6-Tetramethyl-piperidin-1-yl)oxy) or a derivative thereof.

The method is particularly suitable for the preparation of compounds ofgeneral formula (I) in which R⁴ is C(O)OR¹⁰ from compounds of generalformula (II) where R⁴ is also C(O)OR¹⁰, where R¹⁰ is as defined abovebut is especially H, C₁₋₆ alkyl or benzyl.

Compounds of general formula (III) may be prepared from compounds ofgeneral formula (IV):

wherein R¹, R²R⁴ are as defined for general formula (I), R⁵ is asdefined for general formula (II); and

Y is a bond or an alkylene or alkenylene linker group having from 1 to 6carbon atoms and optionally substituted with one or more groups R³,wherein R³ is as defined for general formula (I);

by reduction.

The reduction may be hydrogenation, usually catalytic hydrogenation.Suitable catalysts for the catalytic hydrogenation include apalladium/carbon, palladium/calcium carbonate, palladium/aluminiumoxide, platinum/palladium or Raney nickel catalyst. The reaction may becarried out in an organic solvent, which may be an alcoholic solventsuch as methanol, ethanol or isopropanol; ethyl acetate; pyridine;acetic acid; cyclopentyl methyl ether (CPME) or N,N-dimethylformamide(DMF). The organic solvent may optionally be mixed with a co-solventsuch as acetone or water and/or a base such as triethylamine may also beadded.

The choice of catalyst and solvent affects the ratio of the requiredproduct of general formula (III):

to its isomer of general formula (XXX):

It also affects the rate of conversion of the intermediate of formula(XXXI):

to the product.

More suitably, a palladium/carbon or palladium/calcium carbonatecatalyst is used. Typically, in the catalyst the palladium is present inan amount of 5-10% by weight with respect to the weight of the matrix(where the matrix is the carbon, calcium carbonate etc).

Solvents which give superior ratios of (III):(XXX) include methanol,ethanol and DMF, particularly methanol and DMF.

When methanol is used as the solvent, it may be used alone or in thepresence of a base such as triethylamine. Suitably, the amount oftriethylamine used is a substoichiometric amount, typically 0.1 to 0.5equivalents with respect to the amount of starting material of generalformula (IV).

Methanol in the presence of triethylamine gave a particularly high ratioof the required product of general formula (III) to isomer of generalformula (XXX).

Reactions conducted with methanol as the solvent may be carried out at atemperature of about −30 to 25° C. and the temperature has little effecton the ratio of (III):(XXX).

When DMF is used as a solvent, it may be mixed with a co-solvent such asacetone, TBME, THF, acetonitrile or acetone/water. Optionally, thesolvent contains a base such as triethylamine in a substoichiometricamount, typically 0.1 to 0.5 equivalents with respect to the amount ofstarting material of general formula (IV).

Reactions conducted using DMF as solvent appear to be more sensitive totemperature than reactions carried out in methanol and the ratio of(III):(XXX) decreases with increasing temperature. Suitably, thereforethe reaction is conducted at a temperature of −30 to 0° C., moresuitably −20 to −10° C.

It has been found that the pressure of hydrogen has little effect on theselectivity and therefore the hydrogen pressure is suitably about 1atmosphere.

Similarly dilution does not appear to have a major impact on theselectivity and therefore the solvent may be used in any convenientamount.

Hydrogenation of a compound of formula (IV) will also reduce any alkenebonds, if present, in the linker Y.

Compounds of general formula (IV) may be prepared from compounds ofgeneral formula (V):

wherein R² and R⁴ are as defined in general formula (I), R⁵ is asdefined for general formula (II) and Y is as defined for general formula(IV);

by selective alkylation with an organometallic reagent.

Suitable organometallic reagents include Gilman reagents formed byreaction of an alkyl lithium compound of formula (XXIV):R¹—Li  (XXIV)

wherein R¹ is as defined for general formula (I);

and a copper (I) salt, particularly a copper (I) halide such as copper(I) iodide.

The reaction may be conducted in an organic solvent such astetrahydrofuran, other ethers such as diethylether or a mixture thereof.

Alternatively, the addition can be carried out using Grignard reagentsR¹MgX, where R¹ is as defined for general formula (I) and X is a halide,for example ethylmagnesium bromide and the reaction is suitablyconducted in the presence of a zinc (II) salt such as zinc chloride anda catalytic amount of a copper (I) or copper(II) salt or complex, forexample copper (I) chloride, copper (II) chloride or a copper(I) orcopper (II) acetylacetonate (acac) complex.

The reaction may be carried out in an organic solvent, for example anether such as THF, 2-methyl THF, methyl tert-butyl ether (tBME), diethylether. Surprisingly, the reaction temperature is not particularlysignificant and while in some cases the reaction may be carried out atreduced temperature, for example at about −25 to 0° C., it has also beensuccessfully conducted at higher temperatures of up to about 55° C.

The process for preparing a compound of formula (I) from a compound offormula (II) is new and itself forms a part of the invention.

The method is particularly suitable for the preparation of compounds ofgeneral formula (II) in which R⁴ is C(O)OR¹⁰ from compounds of generalformula (III) where R⁴ is also C(O)OR¹⁰, where R¹⁰ is as defined abovebut is especially H, C₁₋₆ alkyl or benzyl.

Compounds of general formula (V) may be prepared from compounds offormula (VI):

wherein R² and R⁴ are as defined in general formula (I), R⁵ is asdefined for general formula (II) and Y is as defined for general formula(IV);

by oxidation, for example using monoperoxypthalate (MMPP) or3-Chloroperoxybenzoic acid, (mCPBA).

The reaction using MMPP may be carried out in an organic solvent such asethyl acetate and if mCPBA is used, the reaction may be carried out in asolvent such as dichloromethane or toluene. Suitably, the reaction isconducted at or just below the reflux temperature of the solvent.

Compounds of general formula (VI) may be prepared from compounds ofgeneral formula (VII):

wherein R² and R⁴ are as defined in general formula (I), R⁵ is asdefined for general formula (II) and Y is as defined for general formula(IV);

by reaction with an oxidizing agent such as chloranil.

The reaction may be carried out under acidic conditions, for example inthe presence of acetic acid, and in an organic solvent such as toluene.

Some compounds of general formulae (V), (VI) and (VII) are known and,for example Uekawa et al in Biosci. Biotechnol. Biochem., 2004, 68,1332-1337 describe the synthesis of (22E)-3-oxo-4,22-choladien-24-oicacid ethyl ester from stigmasterol followed by its conversion to(22E)-3-oxo-4,6,22-cholatrien-24-oic acid ethyl ester, which has theformula:

Uekawa et al then go on to describe the conversion of this compound to(6α, 7α, 22E)-6,7-epoxy-3-oxo-4,22-choladien-24-oic acid ethyl ester, acompound of general formula (III) in which R² and R⁵ are H, Y is—CH═CH—, and R⁴ is C(O)OCH₂CH₃.

Other compounds of general formulae (V), (VI) and (VII) may be preparedby analogous methods from phytosterols similar to stigmasterol.

Stigmasterol and other phytosterols are plant sterols and are readilyavailable or may be prepared by known routes.

Compounds of general formula (VII) may also be prepared from compoundsof general formula (VIIIa):

wherein R² and R⁴ are as defined in general formula (I), R⁵ is asdefined for general formula (II) and Y is as defined for general formula(IV);

by reaction with lithium bromide and a base such as lithium carbonate.The reaction may be carried out in a solvent such asN,N-dimethylformamide (DMF) and at a temperature of about 120 to 180° C.

Compounds of general formula (VIIIa) may be obtained by bromination of acompound of general formula (VIII):

wherein R² and R⁴ are as defined in general formula (I), R⁵ is asdefined for general formula (II) and Y is as defined for general formula(IV);

using, for example bromine in acetic acid.

Compounds of general formula (X) may be prepared from compounds ofgeneral formula (XI):

wherein R² and R⁴ are as defined in general formula (I), R⁵ is asdefined for general formula (II) and Y is as defined for general formula(IV);

by oxidation, typically with a chromium-based oxidizing agent or withsodium hypochlorite.

Compounds of general formula (IX) in which R⁴ is C(O)OR¹⁰, where R¹⁰ isC₁₋₆ alkyl or benzyl may be prepared from compounds of general formula(VII) in which R⁴ is C(O)OH by esterification, typically by reactionwith an appropriate alcohol under acidic conditions.

Compounds of general formula (IX) in which R⁴ is C(O)OH and R⁵ is H maybe prepared from compounds of general formula (X):

wherein R² and Y are as defined in general formula (I);

R⁴ is C(O)OR¹⁰, where R¹⁰ is C₁₋₆ alkyl or benzyl; and

R¹² is a protected OH;

by reaction with a reducing agent, typically hydrazine under basicconditions and in an alcoholic or glycolic solvent, for examplediethylene glycol.

Where R¹² is a protected OH group which is stable under basicconditions, the reaction may be followed by a reaction to remove theprotecting group R¹² to leave an OH group.

Protecting groups for OH are discussed above and, for example, R¹² maybe a group C(O)R¹⁴, where R¹⁴ is as defined above, in particular, C₁₋₆alkyl or benzyl. Silyl ethers are also suitable, and in this case, R²and/or R⁵ may independently be a group Si(R¹⁶)₃, where R¹⁶ is as definedabove but is especially C₁₋₆ alkyl or phenyl. Other suitable protectinggroups for OH are well known to those of skill in the art (see Wuts, P GM and Greene, T W (2006) “Greene's Protective Groups in OrganicSynthesis”, 4^(th) Edition, John Wiley & Sons, Inc., Hoboken, N.J.,USA).

Particularly suitable R¹² groups include groups which are not stable inthe presence of a base since this removes the need for the additionalstep of removing the protecting group. An example of a group R¹² whichis not stable in basic conditions is a group C(O)R¹⁴, where R¹⁴ is asdefined above, and is particularly C₁₋₆ alkyl or benzyl.

Alternatively, the reaction may be carried out in 2 steps such that thecompound of general formula (IX) is reacted with a compound of generalformula (XXXII):R²⁰—NH—NH₂  (XXXII)wherein R²⁰ is a leaving group such as toluene sulfonyl or methanesulfonyl;

to give a compound of general formula (XXXIII):

followed by reduction with a suitable reducing agent. Examples ofreducing agents which can be used in this reaction include hydrides suchas sodium borohydride, sodium cyanoborohydride, lithium aluminum hydrideetc.

Compounds of general formula (X) may be prepared from compounds ofgeneral formula (XI):

wherein R² is as defined in general formula (I) and Y is as defined forgeneral formula (IV);

R⁴ is C(O)OR¹⁰, where R¹⁰ is C₁₋₆ alkyl or benzyl; and

R¹² is as defined above, especially —C(O)C₁₋₆ alkyl;

by reaction with an oxidizing agent, for example sodium hypochlorite.

The reaction may be carried out under acidic conditions, for example inthe presence of acetic acid, and in an organic solvent such as ethylacetate.

Compounds of general formula (XI) may be prepared from compounds ofgeneral formula (XII):

wherein R² is as defined in general formula (I) and Y is as defined forgeneral formula (IV);

R⁴ is C(O)OR¹⁰, where R¹⁰ is C₁₋₆ alkyl or benzyl;

by reaction with an agent suitable to introduce the protecting group R¹²For example, when R¹² is C(O)R¹⁴, the compound of general formula (XII)may be reacted with a carboxylic acid anhydride or an acid chloride inthe presence of a weak base such as pyridine, suitably catalysed by4-dimethylaminopyridine (DMAP). The reaction may be conducted in asolvent such as ethyl acetate.

Compounds of general formula (XII) may be prepared by the esterificationof compounds of general formula (XIII):

wherein R² is as defined in general formula (I) and Y is as defined forgeneral formula (IV);

The reaction may be carried out by reacting the acid of general formula(XIII) with a suitable alcohol under acidic conditions.

Compounds of general formula (XIII) are known. For example, the compoundof general formula (XIII) in which Y is —CH₂CH₂— and R² is H isdeoxycholic acid, which is readily available from a number of sources.

Other bile acids with different values for Y and R² can be used asalternative starting materials.

An alternative route to compounds of general formula (VII) is as shownin Scheme 1 in which androstenedione is converted to a compound ofgeneral formula (V) in which R² and R⁵ are H; R⁴ is —C(O)OCH₃ and Y iseither —CH₂CH₂— or —CH═CH—.

An alternative route to compounds of general formula (VI) in which Y isan alkenylene group is by use of an olefination reaction, for example aHorner-Wadsworth-Emmons (HWE) olefination of a compound of generalformula (XIV):

wherein R² is as defined in general formula (I) and R⁵ is as defined forgeneral formula (II);

using a compound of general formula (XV):

wherein R¹⁰ is as defined for general formula (I).

The reaction may be carried out under standard HWE conditions, forexample using a base such as sodium hydride.

Compounds of general formula (XV) are readily available or may beprepared by methods known to those of skill in the art.

Other olefination reactions such as a Tebbe olefination, a Wittigreaction or a Julia-Kocienski olefination would also give rise tocompounds of general formula (III) in which Y is an alkenylene group.These olefination reactions are familiar to a chemist of skill in theart.

Compounds of general formula (XIV) may be prepared by reaction of acompound of general formula (XVI) with ozone

wherein R² is as defined for general formula (I), R⁵ is as defined forgeneral formula (II) and R¹⁵ is C₁₋₆ alkyl.

An example of a reaction of this type is given in U.S. Pat. No.2,624,748.

Compounds of general formula (XVI) may be prepared by reaction of acompound of general formula (XVII):

wherein R² is as defined for general formula (I), R⁵ is as defined forgeneral formula (II) and R¹⁵ is C₁₋₆ alkyl;

with an acid in a solvent such as methanol.

Compounds of general formula (XVII) may be prepared by oxidation of acompound of general formula (XVIII):

wherein R² and R⁵ are as defined for general formula (I) and R¹⁵ is C₁₋₆alkyl using an Oppenauer oxidation.

Examples of the conversion of compounds of general formula (XVIII) tocompounds of general formula (XVI) are taught by Shepherd et al, J. Am.Chem. Soc. 1955, 77, 1212-1215 and Goldstein, J. Med. Chem. 1996, 39,5092-5099.

One example of a compound of general formula (XVI) is ergosterol, whichis a fungal sterol and Scheme 2 below shows the conversion of ergosterolto a compound of general formula (IV) in which both R² and R⁵ are H, Yis CH═CH₂ and R⁴ is C(O)OR¹⁰, where R¹⁰ is ethyl.

As with the compounds of general formula (I), compounds of generalformulae (II) to (XIII), (VIIIa) and (XXXIII) in which R⁴ is C(O)R¹⁰,C(O)NR¹⁰R¹¹, S(O)R¹⁰, SO₃R¹⁰, or OSO₃R¹⁰ may be prepared from thecorresponding compounds in which R⁴ is C(O)OR¹⁰ by reaction with anappropriate reagents using methods well known to those of skill in theart. For example, the methods described in WO2008/002573 andWO2010/014836 or methods similar to those described by Classon et al, J.Org. Chem., 1988, 53, 6126-6130 and Festa et al, J. Med. Chem., 2014,57, 8477-8495.

Compounds of general formula (I) are synthetic precursors of compoundsof general formula (XXI):

wherein R¹, R⁴ and Y¹ are as defined in general formula (I);

R² is H, halo or OH; and

R^(5a) is H or OH.

The compounds of general formula (I) may be converted to compounds ofgeneral formula (XXI) as described below, which is itself a part of theinvention.

Therefore, in a further aspect of the invention there is provided aprocess for the preparation of a compound of general formula (XXI), theprocess comprising:

i. reduction of the compound of general formula (I) using a suitablereducing agent and, where R² and/or R^(5b) is a protected OH, removal ofthe protecting group(s), to give a compound of general formula (XXI) asdefined above, wherein removal of the protecting group can take placebefore or after the reduction; and optionally

iii. conversion of a compound of general formula (XXI) to anothercompound of general formula (XXI).

Compounds of general formula (XXI) are potent agonists of FXR and TGR5and include obeticholic acid, which is a compound of formula (XXI) inwhich R¹ is ethyl, R² and R^(5a) are both H, Y¹ is —CH₂CH₂—, and R⁴ isC(O)OH.

In the compounds of general formulae (XIX) to (XXI), more suitablevalues for Y¹, R¹ and R⁴ are as defined for general formula (I).

The reducing agent is typically a hydride, such as sodium borohydridewhich may be used in a solvent such as a mixture of tetrahydrofuran andwater. Typically, this reaction is carried out under basic conditions,for example in the presence of a strong base such as sodium or potassiumhydroxide and at a temperature of about about 0 to 110° C., more usually60 to 100° C. A compound of general formula (XXI) in which R⁴ is C(O)OHmay be produced by the reduction of a compound of general formula (I) inwhich R⁴ is C(O)OH.

Compounds of general formula (XXI) in which R⁴ is C(O)R¹⁰, C(O)NR¹⁰R¹¹,S(O)R¹⁰, SO₂R¹⁰, or OSO₂R¹⁰ may be prepared from the correspondingcompounds in which R⁴ is C(O)OR¹⁰ by reaction with an appropriatereagents using methods well known to those of skill in the art.

Compounds of general formula (XXI) in which R⁴ is SO₃R¹⁰ may besynthesised from compounds of general formula (XXI) in which R⁴ isC(O)OH by the methods taught in WO2008/002573, WO2010/014836 andWO2014/066819.

Thus a compound of formula (XXI) in which R⁴ is C(O)OH may be reactedwith a C₁₋₆ alkanoyl or benzoyl chloride or with a C₁₋₆ alkanoicanhydride to protect the OH groups. The protected compound may then bereacted with a reducing agent such as a hydride, suitably sodiumborohydride in order to reduce the carboxylic acid group to OH. Thealcohol group may be replaced by a halogen, for example bromine oriodine, using the triphenyl phosphine/imidazole/halogen method describedby Classon et al, J. Org. Chem., 1988, 53, 6126-6130. The halogenatedcompound may then be reacted with sodium sulphite in an alcoholicsolvent to give a compound with a SO₃ ⁻Na⁺ substituent.

Compounds of general formula (XXI) in which R⁴ is OSO₃R¹⁰ can beobtained by reacting the alcohol obtained from reducing the protectedcarboxylic acid with chlorosulfuric acid in the presence of a base suchas triethylamine to yield the protected triethylammonium salt.Protecting groups can be removed using base hydrolysis as describedabove. Reduction of the carboxylic acid followed by reaction of theresultant alcohol with chlorosulfurous acid yields a compound of generalformula in which R⁴ is OSO₂R¹⁰.

Compounds of general formula (XXI) in which R⁴ is C(O)NR¹⁰R¹¹ may beprepared from the carboxylic acid by reaction with an amine of formulaH—NR¹⁰R¹¹ in a suitable solvent with heating. Compounds of generalformulae (XIX) to (XXI) in which R⁴ is C(O)NR¹⁰R¹¹ or OSO₃R¹⁰ may alsobe prepared by methods similar to those described by Festa et al, J.Med. Chem., 2014, 57 (20), 8477-8495. These methods also form an aspectof the invention.

A compound of general formula (XXI) in which R⁴ is C(O)R¹⁰ can beobtained by reduction of a compound in which R⁴ is C(O)OR¹⁰ using oneequivalent of diisobutyl aluminium hydride (DIBAL) to obtain an aldehydein which R⁴ is C(O)H (see, for example, WO2011/014661).

Alternatively, the aldehyde may be prepared by oxidation of a protectedcompound in which R⁴ is OH prepared as described above. The oxidationmay be Swern oxidation carried out using oxalyl chloride and dimethylsulfoxide followed by trimethylamine (see, for example Xiang-Dong Zhouet al, Tetrahedron, 2002, 58, 10293-10299). Alternatively, the oxidationmay be carried out using an oxidating agent such as pyridiniumchlorochromate (PCC) as described by Carnell et al (J. Med. Chem., 2007,50, 2700-2707).

A compound of general formula (I) in which R⁴ is C(O)R¹⁰ where R¹⁰ isother than hydrogen can be obtained by known methods, for example by thereaction of the aldehyde in which R⁴ is C(O)H with a suitable Grignardreagent, followed by oxidation. Such methods are well known to those ofskill in the art.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an image showing the chemical structure of (6β, 7α,22E)-6-ethyl-7-hydroxy-3-oxo-4,22-choladien-24-oic acid ethyl ester.

FIG. 2 is an image showing the chemical structure of (6α,5β)-3,7-dioxo-6-ethyl-cholan-24-oic acid.

The invention will now be described in greater detail with reference tothe examples.

In the examples, the following abbreviations were used:

AcOH Acetic acid

CPME Cyclopentyl methyl ether

DMF N,N-dimethylformamide

EtOAc Ethyl acetate

EtOH Ethanol

IPA Isopropyl alcohol

MeOH Methanol

NEt₃ Triethylamine

nBuOAc n-butyl acetate

TBME t-butyl methyl ether

THF Tetrahydrofuran

TLC Thin layer chromatography

EXAMPLES 1 to 4 Synthesis of (6β, 5β,7α)-6-ethyl-7-hydroxy-3-oxo-cholan-24-oic acid ethyl ester fromStigmasterol Example 1—Synthesis of (22E)-3-oxo-4,6,22-cholatrien-24-oicacid ethyl ester

The starting material, (22E)-3-oxo-4,22-choladien-24-oic acid ethylester, was prepared from stigmasterol according to the method describedby Uekawa et al in Biosci. Biotechnol. Biochem., 2004, 68, 1332-1337.

(22E)-3-oxo-4,22-choladien-24-oic acid ethyl ester (1.00 kg, 2.509 mol;1 eq) was charged to a reaction vessel, followed by AcOH (3 vol, 3.0 L)and toluene (1 vol, 1.0 L) with stirring. Chloranil (0.68 kg, 2.766 mol;1.1 eq) was then charged and the reaction mixture heated to 100° C. andmaintained at this temperature for 1-2 h (IPC by TLC on silica, eluent3:7 EtOAc:Heptane; Starting Material: R_(f) 0.50, Product: R_(f) 0.46;visualise with anisaldehyde stain). The mixture was then cooled in anice/water bath to 10° C. and the resulting solid was filtered off. Thefilter-cake was washed with premixed 3:1 AcOH:Toluene (4×0.5 vol) at 5°C.±4° C. and the filtrate concentrated in vacuo at up to 70° C. Theresidue was dissolved in acetone (3 vol), then 3% w/w aq. NaOH (10 vol)was charged dropwise with stirring, maintaining the temperature below30° C. (exothermic). The resulting suspension was cooled to 10-15° C.and stirred for 30 mins. The solids were collected by filtration and thefilter cake was washed with premixed 1:1 acetone:water (1×2 vol then 3×1vol). The filter cake (tan solid) was dried under vacuum at 70-75° C.,672 g (68% yield). Characterisation of the compound agrees with the datapublished in the literature.

Example 2—(6α, 7α, 22E)-6,7-epoxy-3-oxo-4,22-choladien-24-oic acid ethylester

To a solution of (22E)-3-oxo-4,6,22-cholatrien-24-oic acid ethyl ester(58.0 g, 146.3 mmol) in EtOAc (1.0 L) at reflux was added 80% MMPP(magnesium bis(monoperoxyphthalate) hexahydrate, 197.0 g, ca. 318.6mmol) in four equal portions at 30 min intervals. The suspension wasvigorously stirred at reflux for 5 h and at ambient temperature for afurther 16 h. The reaction was then heated to reflux and stirred for anadditional 6 h. The mixture was cooled to ca. 50° C. and the solids werefiltered and rinsed with hot EtOAc (200 mL). The filtrate wassubsequently washed with 20% aq. NaHSO₃ (100 mL), 1M aq. NaOH (100 mLthen 200 mL) and 10% aq. NaCl (250 mL), dried over Na₂SO₄, filtered andconcentrated in vacuo. The residue (yellow solid) was crystallised fromminimum volume of EtOAc at 60° C. to give the epoxide product as offwhite/pale yellow crystals (25.7 g, 43% yield, prisms). Characterisationof the compound agrees with the data published in the literature.

Example 3—Synthesis of (6β, 7α,22E)-6-ethyl-7-hydroxy-3-oxo-4,22-choladien-24-oic acid ethyl ester

Method 1:

To a suspension of Cul (1.40 g, 7.35 mmol) in diethyl ether (10 mL),cooled to −78° C. under an argon blanket was charged EtLi (28.8 mL, 14.4mmol, 0.5 M solution in benzene/cyclohexane). The thick white suspensionformed was allowed to warm to 0° C., stirred for 5 mins (forming a darksolution) and cooled to −78° C. A solution of (6α, 7α,22E)-6,7-epoxy-3-oxo-4,22-choladien-24-oic acid ethyl ester (1.00 g,2.42 mmol) in diethyl ether/THF (24 mL, 3:1) was prepared and charged tothe vessel containing the organocuprate. THF (1 mL) was used to rinsethe vessel that contained the solution of the epoxide and this was alsocharged to the organocuprate. The reaction mixture was allowed to warmto −4° C. over 30 mins after which time the reaction was complete by TLC(silica, 1:1 EtOAc:heptane). After a further 30 mins of stirring at c.a.−4° C. a solution of aq. sat. NH₄Cl was charged and the mixture wasstirred over 30 mins. The mixture was transferred to a separating funneland the aqueous phase was removed, along with solid material present atthe interface. The organic phase was washed with 5 wt % aq NaHCO₃ (2×50mL) and water (1×50 mL). TBME (50 mL) was used to extract the originalaqueous phase from the reaction and the combined washes. The combinedorganic phases were concentrated and the residue was purified bychromatography using silica (25 g) as the stationary phase (gradientelution with 0-30% EtOAc in heptane) to give (6β, 7α,22E)-6-ethyl-7-hydroxy-3-oxo-4,22-choladien-24-oic acid ethyl ester(0.63 g, 59%) (FIG. 1).

¹H NMR (400 MHz, CDCl₃): δ=6.82 (1H, dd, J=15.6, 8.9, C22H), 5.75 (1H,s, C4H), 5.74 (1H, d, J=15.6, C23H), 4.17 (2H, q, J=7.1, OCH₂CH₃), 3.72(1H, br s, C7H), 2.52-2.25 (5H, m), 2.05-1.98 (2H, m), 1.82-1.10 (23H,m), 0.91 (3H, t, J=7.4, CH3), 0.77 (3H, s, CH3). ¹³C NMR (100 MHz,CDCl₃): δ=199.2, 171.2, 167.1, 154.5, 128.4, 119.0, 71.9, 60.1, 55.3,54.9, 49.9, 44.3, 42.7, 39.6, 39.1, 38.3, 37.4, 35.6, 34.0, 28.0, 26.3,23.6, 20.8, 19.7, 19.2, 14.2, 12.8, 12.0; (IR) v_(max)(cm⁻¹): 3467,2939, 2870, 1716, 1651, 1457, 1268, 1229, 1034; HRMS (ESI-TOF) m/z:(M+H)⁺ calcd for C₂₈H₄₃O₄ 443.3161; found: 443.3156. mp=59.4-62.9° C.

Method 2

ZnCl₂ (32.84 g, 240.9 mmol) was dried under vacuum with slow stirring at180° C. for 2 h. The flask was cooled to room temperature under an argonatmosphere and the residue was dissolved in THF (520 mL) and transferredvia cannula into a three neck reaction flask equipped with mechanicalstirrer and temperature probe. The solution was cooled in an ice bath to0-3° C. and a 3M solution of EtMgBr in Et₂O (80 mL, 240.0 mmol) wasadded dropwise over 20 mins, maintaining the internal temperature below10° C. Formation of a white precipitate (active zincate species) wasobserved after addition of ca. ⅓ of the Grignard solution. The mixturewas stirred for 1.2 h at 0° C. before a solution of the epoxide (6α, 7α,22E)-6,7-epoxy-3-oxo-4,22-choladien-24-oic acid ethyl ester (43.0 g,104.2 mmol) in THF (300 mL) was added dropwise, maintaining the internaltemperature below 10° C. Solid CuCl (1.03 g, 0.104 mmol) was then addedin two equal portions with vigorous stirring. After 10 mins the coolingbath was removed and stirring continued at ambient temperature for anadditional 1.2 h. The reaction was quenched by dropwise addition of sat.aq. NH₄Cl (800 mL) at <15° C. and stirred for 0.5 h. The mixture wasfiltered and the solid rinsed with TBME (150 mL). The phases wereseparated and the aqueous phase extracted with TBME 2×250 mL. Thecombined organic extracts were washed with 10% aq. NaCl (2×200 mL),dried over Na₂SO₄, filtered and concentrated in vacuo to give 43.7 g ofthe crude (6β, 7α, 22E)-6-ethyl-7-hydroxy-3-oxo-4,22-choladien-24-oicacid ethyl ester as a yellow foam.

Method 3

To a solution of ZnCl₂ in THF (0.5 M, 8.7 mL, 4.85 mmol, 0.9 eq) wascharged anhydrous THF (8.0 mL) and the contents then cooled to −25° C. Asolution of EtMgBr in TBME (1.0 M, 8.7 mL, 8.70 mmol, 1.8 eq) was addedover 30 mins and the mixture stirred for 45 mins at −25° C. Solid CuCl(24 mg, 0.49 mmol, 0.05 eq) was added in one portion and a solution of(6α, 7α, 22E)-6,7-epoxy-3-oxo-4,22-choladien-24-oic acid ethyl ester(2.0 g, 4.85 mmol) in THF (8.0 mL) was added dropwise over 30 mins. Theremaining solid CuCl (24 mg, 0.49 mmol, 0.05 eq) was added half waythrough the addition of (6α, 7α,22E)-6,7-epoxy-3-oxo-4,22-choladien-24-oic acid ethyl ester. Thereaction was stirred for 1 h at −25° C., (TLC 1:1 Heptane:EtOAc,visualised by UV and developed using Ceric Ammonium Molybdate stain) andthen additional of EtMgBr in TBME (1.0 M, 2.9 mL, 2.91 mmol, 0.6 eq) wasadded over 10 mins. The reaction was stirred for 0.5 h at −25° C. andthen quenched by the addition of sat. aq. NH₄Cl (5 mL), maintaining thetemperature below −5° C. The inorganic salts were filtered off, rinsedwith TBME and the filtrate phases were separated. The aqueous layerextracted with TBME and then the combined organic extracts were washedwith sat. aq. NH₄Cl (3×5 mL) and 10% brine (3×6 mL). The organic phasewas concentrated in vacuo at 40° C. to give crude (6β, 7α,22E)-6-ethyl-7-hydroxy-3-oxo-4,22-choladien-24-oic acid ethyl ester as ayellow foam (1.91 g).

Method 4

To a solution of ZnCl₂ in THF (0.5 M, 8.7 mL, 4.85 mmol, 0.9 eq) wascharged anhydrous THF (8.0 mL) and the contents then heated to 40° C. Asolution of EtMgBr in TBME (1.0 M, 8.7 mL, 8.70 mmol, 1.8 eq) was addedover 30 mins and the mixture stirred for 45 mins at 40° C. Solid CuCl(24 mg, 0.49 mmol, 0.05 eq) was added in one portion and a solution of(6α, 7α, 22E)-6,7-epoxy-3-oxo-4,22-choladien-24-oic acid ethyl ester(2.0 g, 4.85 mmol) in THF (8.0 mL) was added dropwise over 30 mins. Theremaining solid CuCl (24 mg, 0.49 mmol, 0.05 eq) was added half waythrough the addition of (6α, 7α,22E)-6,7-epoxy-3-oxo-4,22-choladien-24-oic acid ethyl ester. Thereaction was stirred for 1 h at 40° C., (TLC 1:1 Heptane:EtOAc,visualised by UV and developed using Ceric Ammonium Molybdate stain) andthen quenched by the dropwise addition of sat. aq. NH₄Cl (5 mL). Theinorganic salts were filtered off, rinsed with TBME and the filtratephases were separated. The aqueous layer was extracted with TBME andthen the combined organic extracts were washed with sat. aq. NH₄Cl (3×5mL) and 10% brine (3×6 mL). The organic phase was concentrated in vacuoat 40° C. to give crude (6β, 7α, 22E)-6-ethyl-7-hydroxy-3-oxo-4,22-choladien-24-oic acid ethyl ester as ayellow foam (2.08 g).

Method 5

To a solution of ZnCl₂ in THF (0.5 M, 8.7 mL, 4.85 mmol, 0.9 eq) wascharged anhydrous THF (8.0 mL) and the contents then cooled to −15° C. Asolution of EtMgBr in THF (1.0 M, 8.7 mL, 8.70 mmol, 1.8 eq) was addedover 30 mins and the mixture stirred for 45 mins at −15° C. Solid CuCl(24 mg, 0.49 mmol, 0.05 eq) was added in one portion and a solution of(6α, 7α, 22E)-6,7-epoxy-3-oxo-4,22-choladien-24-oic acid ethyl ester(2.0 g, 4.85 mmol) in THF (8.0 mL) was added dropwise over 30 mins. Theremaining solid CuCl (24 mg, 0.49 mmol, 0.05 eq) was added half waythrough the addition of (6α,7α,22E)-6,7-epoxy-3-oxo-4,22-choladien-24-oic acid ethyl ester. Thereaction stirred for 1 h at −15° C., (TLC 1:1 Heptane:EtOAc, visualisedby UV and developed using Ceric Ammonium Molybdate stain) and thenadditional EtMgBr in THF (1.0 M, 4.35 mL, 4.36 mmol, 0.9 eq) was addedover 15 mins and then quenched by the dropwise addition of sat. aq.NH₄Cl (5 mL). The inorganic salts were filtered off, rinsed with TBMEand the filtrate phases were separated. The aqueous phase was extractedwith TBME and then the combined organic extracts were washed with sat.aq. NH₄Cl (3×5 mL) and 10% brine (3×6 mL). The organic phase wasconcentrated in vacuo at 40° C. to give crude (6β, 7α,22E)-6-ethyl-7-hydroxy-3-oxo-4,22-choladien-24-oic acid ethyl ester as ayellow foam (1.94 g).

Example 4—Synthesis of (6β, 5β,7α)-6-ethyl-7-hydroxy-3-oxo-cholan-24-oic acid ethyl ester

Method 1

To a suspension of 10 wt. % Pd/C (50% wet, 20 mg, 8.6 mol %) in DMF (2mL) was added a solution of (6β, 7α,22E)-6-ethyl-7-hydroxy-3-oxo-4,22-choladien-24-oic acid ethyl ester (50mg, 0.11 mmol) in DMF (3 mL) and the reaction mixture was cooled to 0°C. The flask was evacuated then filled with hydrogen three times withvigorous stirring. After 3 h the flask was evacuated then filled withargon and the mixture filtered via syringe filter. The mixture waspartitioned between TBME (30 mL) and H₂O (20 mL). The organic phase wasdried (Na₂SO₄) and concentrated in vacuo. The crude product (50 mg) wasa 14:1 mixture of 5β to 5α isomers (analysed by ¹H NMR) of (6β, 5β,7α)-6-ethyl-7-hydroxy-3-oxo-cholan-24-oic acid ethyl ester, yield 92%.

¹H NMR (700 MHz, CDCl₃): δ=4.12 (2H, q, J=7.1, OCH₂CH₃), 3.71 (1H, br s,C7H), 3.34 (1H, dd, J=15.5, 13.6, C4H), 2.39-2.32 (2H, m), 2.24-2.20(1H, m), 2.14-2.09 (2H, m), 2.03-1.91 (4H, m), 1.83-1.79 (2H, m),1.68-1.63 (2H, m), 1.58 (1H, s), 1.55-1.12 (19H, m), 1.04 (3H, s),0.95-0.93 (6H, m), 0.88 (1H, J=7.0), 0.71 (3H, s). ¹³C NMR (100 MHz,CDCl₃): δ=213.5, 174.2, 72.1, 60.2, 55.9, 50.2, 49.8, 47.0, 46.7, 42.7,39.5, 37.7, 36.3, 36.0, 35.7, 35.3, 34.2, 31.3, 31.0, 28.1, 27.7, 24.4,23.8, 20.8, 18.3, 14.2, 13.9, 11.8. (IR) v_(max)(cm⁻): 3514, 2939, 2870,1710, 1462, 1377, 1159, 1099, 1032; HRMS (ESI-TOF) m/z: (M−H₂O+H)⁺ calcdfor C₂₈H₄₅O₃ 429.3369; found: 429.3363.

Method 2

(6β, 7α, 22E)-6-ethyl-7-hydroxy-3-oxo-4,22-choladien-24-oic acid ethylester (20.0 g) was dissolved in DMF (400 mL) and added under argon tosolid 10 wt. % Pd/C (50% wet, 10.0 g). The mixture was cooled in anice-salt bath to approximately −15° C. and the flask was evacuated thenfilled with hydrogen three times with vigorous stirring. The mixture wasstirred under an atmosphere of hydrogen for 6 h then the flask wasevacuated, filled with argon and filtered through a pad of celite. Thecatalyst was rinsed with 400 mL of TBME. The filtrate was washed with10% aq. NaCl (400 mL) and the aqueous phase extracted with TBME (400mL). The combined organic phases were washed with 10% aq. NaCl (3×200mL), dried over Na₂SO₄, filtered and concentrated in vacuo to give crude(6β, 5β, 7α)-6-ethyl-7-hydroxy-3-oxo-cholan-24-oic acid ethyl ester(20.0 g, ca. 28:1 5Hβ:5Hα ratio) as pale yellow oil.

Method 3

10% Pd/C was charged to a stainless steel jacketed reaction vessel underan argon atmosphere; DMF was added (20 mL), followed by a solution ofcrude (6β, 7α, 22E)-6-ethyl-7-hydroxy-3-oxo-4,22-choladien-24-oic acidethyl ester from Example 3 (approximately 72.6 mmol) in DMF (130 mL).The reaction mixture was cooled to −25° C. (over approximately 40 mins)with vigorous stirring (1200 rpm). The reaction vessel was evacuated andcharged with hydrogen (10-12 bar) three times. The mixture was stirredfor 16 h under an atmosphere of hydrogen (10-12 bar). The vessel wasevacuated, purged with argon and warmed to 20° C. with stirring. TLC ofthe reaction mixture (1:1 Heptane:EtOAc, developed using Ceric AmmoniumMolybdate or vanillin dip, Rf values: starting material=0.42,product=0.67) indicated complete consumption of the starting material.The suspension was diluted with CH₃CN (120 mL) and H₂O (30 mL) and thesuspension filtered via a double GFA filter paper and the filter cakerinsed with CH₃CN (60 mL). The mixture was telescoped to the next stepwithout further purification. The mixture contained approximately 5% ofthe 5H-α isomer.

Optimisation

The hydrogenation reaction of this example proceeds via the intermediateshown below and produces both the required 5Hβ compound and its 5Hαisomer. A solvent and catalyst screen was carried out to determinereaction conditions which led to the highest yield and the highestratios of 5Hβ isomer to 5Hα isomer.

The solvent screen was performed using 10 wt. % Pd/C catalyst and thereactions were run at room temperature under atmospheric pressure ofhydrogen. The reaction run in MeOH in the presence of NEt₃ was moreselective than the one run in neat MeOH, whilst the addition of 10% ofH₂O decreased the 5βH selectivity. The reaction in DMF provided the bestβ:α ratio. The reaction in pyridine gave poor conversion to the requiredproduct with mainly starting material and intermediate present in themixture.

Solvent 5 H β:α ratio A MeOH 4:1 B MeOH:H₂O 2:1 C MeOH:NEt₃ 7:1 D EtOH3:1 E IPA 2:1 F EtOAc 2:1 G Pyridine 2:1 H AcOH 1:1 I CPME 1:1 J DMF 9:1

Reactions in DMF and MeOH were tested at a range of temperatures. Forreactions run in DMF temperature has substantial impact on selectivity(the selectivity decreases with increasing temperature), while littledifference was observed for reactions in MeOH.

Reactions in DMF and MeOH were tested at a range of commerciallyavailable 5 and 10 wt. % Pd catalysts, on carbon, calcium carbonate,barium sulfate and aluminium oxide support.

The reactions were run in 10 volumes of solvent at −15° C. underatmospheric pressure of hydrogen gas. For reactions run in DMF pressurehas lower impact on the selectivity than the temperature. The effect ofdilution on the selectivity is negligible.

Examples 5 to 14 Synthesis of (6β, 5β,7α)-6-ethyl-7-hydroxy-3-oxo-cholan-24-oic acid ethyl ester fromDeoxycholic Acid Example 5—Synthesis of (3α,5β)-3-acetoxy-12-oxo-cholan-24-oic acid methyl ester

To a solution of deoxycholic acid (500 g, 1.27 mol) in MeOH (1.5 L) wascharged H₂SO₄ (0.68 mL, 12.7 mmol) and the reaction heated to 64° C.until complete. The reaction was cooled to 55° C. and pyridine (2.06 mL,25.4 mmol) was charged. MeOH (800 mL) was removed by distillation andthe reaction cooled to 50° C. EtOAc (500 mL) was charged and thedistillation continued. This co-evaporation was repeated until the MeOHcontent was <0.5%. The reaction was cooled to 40° C. and EtOAc (1.0 L)was charged followed by Pyridine (134 mL, 1.65 mol) and DMAP (1.1 g,8.89 mmol). Acetic anhydride (150 mL, 1.58 mmol) was added dropwise andthe reaction vessel stirred at 40° C. until complete. The reaction wascooled to 22° C. and 2M aq. H₂SO₄ (1500 mL) added maintaining thetemperature below 25° C. The aqueous phase was removed and the organicphase washed with water (1.2 L), sat. aq. NaHCO₃ solution (1.2 L×2) andwater (1.2 L). AcOH (1.0 L) was charged to the organic layer, followedby NaBr (6.6 g, 63.5 mmol). Aq. 16.4% NaOCl solution (958 mL, 2.54 mol)was charged dropwise maintaining the reaction temperature below 25° C.The reaction was stirred until complete, then cooled to 10° C. andstirred for 90 mins. The resulting solids were collected by filtration,washed with water (3×500 mL) and the filter cake dried under vacuum at40° C. The solids were crystallised from MeOH (10 vol) to give (3α,5β)-3-acetoxy-12-oxo-cholan-24-oic acid methyl ester as an off whitesolid (268 g).

Example 6—Synthesis of (3α, 5β)-3-acetoxy-cholan-24-oic acid methylester

(3α, 5β)-3-acetoxy-12-oxo-cholan-24-oic acid methyl ester (268 g, 0.6mol) was charged to the reaction vessel under argon, followed by AcOH(1.8 L). Tosyl hydrazide (190 g, 1.02 mol) was then added maintainingthe reaction temperature at 25° C. The reaction was stirred untilcomplete and then NaBH₄ (113.5 g, 3.00 mol) was charged portion-wisemaintaining the temperature below 25° C. The reaction mixture wasstirred until complete and then quenched by the dropwise addition ofwater (1.34 L) maintaining the temperature below 25° C. The reactionmixture was stirred for 30 mins, the resulting solids collected byfiltration, washed with water (3×270 mL) and the solid dried undervacuum at 40° C. The solids were crystallised from MeOH (3 vol) to give(3α, 5β)-3-acetoxy-cholan-24-oic acid methyl ester as an off white solid(214.5 g).

Example 7—Synthesis of (3α, 5β)-3-hydroxy-cholan-24-oic acid(Lithocholic Acid)

To a solution of (3α, 5β)-3-acetoxy-cholan-24-oic acid methyl ester(214.5 g, 0.50 mol) in IPA (536 mL) was charged water (536 mL) and 50%w/w NaOH (99 g, 1.24 mol). The reaction was heated to 50° C. and stirreduntil complete. 2M H₂SO₄ was charged slowly with vigorous stirring untilpH 2-3 was obtained and then the reaction cooled to 20° C. The resultingsolids were collected by filtration, washed with water (3×215 mL) andthe resultant solid dried under vacuum at 40° C. to give (3α,5β)-3-hydroxy-cholan-24-oic acid (176.53 g)

Example 8—Synthesis of (5β)-3-oxocholan-24-oic acid ethyl ester

To a solution of (3α, 5β)-3-hydroxy-cholan-24-oic acid (10 g, 26.5 mmol)in EtOH (50 mL) was charged H₂SO₄ 96% (14 μL, 0.27 mmol) and thereaction mixture then heated to reflux for 16 h. Pyridine was thencharged, the mixture stirred for 30 mins and concentrated in vacuo at40° C. The residue was dissolved in EtOAc (30 mL) and AcOH (10 mL) andNaBr (136 mg, 1.33 mmol) was then charged. The solution was cooled to 5°C. and NaOCl 9% (27 mL, 39.8 mmol) was charged dropwise maintaining thetemperature below 10° C. The resulting suspension was warmed to ambienttemperature and stirred for 1 h. The reaction mixture was cooled to 0°C. for 10 mins, the solids collected by filtration and washed with water(3×3 vol). The resultant solid was dried under vacuum at 40° C. to give(5β)-3-oxocholan-24-oic acid ethyl ester (7.83 g).

Example 9—Synthesis of (4α, 5β)-3-oxo-4-bromo-cholan-24-oic acid ethylester

To a solution of (5β)-3-oxocholan-24-oic acid ethyl ester (8.0 g, 19.9mmol) in AcOH (84 mL) was added Br₂ in AcOH (16 mL, 21.9 mmol) dropwiseover 15 mins. The reaction mixture was stirred for 10 mins, then dilutedwith EtOAc (250 mL), washed with water (2×200 mL) and concentrated invacuo at 40° C. The crude material was purified by column chromatography(30% Heptane:EtOAc) and concentrated in vacuo at 40° C. to give (4α,5β)-3-oxo-4-bromo-cholan-24-oic acid ethyl ester as a pale crystallinesolid (7.49 g).

Example 10—Synthesis of (5(3)-3-oxo-4-cholene-24-oic acid ethyl ester

To a solution of (4α, 5β)-3-oxo-4-bromo-cholan-24-oic acid ethyl ester(4.0 g, 8.33 mmol) in DMF (40 mL) was charged Li₂CO₃ (4.0 g, 1 mass eq)and LiBr (2.0 g, 0.5 mass eq). The mixture was heated to 150° C. for 2 hthen allowed to cool to ambient temperature and poured onto a mixture ofwater and ice (200 g, 50 volumes) and AcOH (8 mL). The resultingsuspension was stirred for 15 mins, the solids collected by filtrationand then purified by column chromatography (30% Heptane:EtOAc) to give3-oxo-4-cholene-24-oic acid ethyl ester as a pale crystalline solid(1.68 g).

Example 11—Synthesis of 3-oxo-4,6-choladien-24-oic acid ethyl ester

3-oxo-4-cholene-24-oic acid ethyl ester (2.23 g, 5.57 mmol) was chargedto a reaction vessel, followed by AcOH (6.7 mL) and toluene (2.23 mL).Chloranil (1.5 g, 6.13 mmol) was charged and the reaction mixture heatedto 100° C. for 2 h (IPC by TLC, 3:7 EtOAc:Heptane; visualized withAnisaldehyde stain). The reaction mixture was cooled to 10° C. for 10mins and the resulting solid removed by filtration. The filter cake waswashed with DCM (9 vol) and the resulting filtrate then concentrated invacuo at 40° C. The residue was dissolved in acetone (9 vol) then 3% w/waq. NaOH (27 vol) was added dropwise maintaining the temperature below30° C. The resulting mixture was cooled in an ice bath for 10 mins andthe solids collected by filtration. The filter cake was washed withwater (2×9 vol) and acetone:water 2:1 (4 vol). Purification by columnchromatography (0-30% Heptane:EtOAc) gave 3-oxo-4,6-choladien-24-oicacid ethyl ester as a pale crystalline solid (1.45 g)

Example 12—Synthesis of (6α, 7α)-6,7-epoxy-3-oxo-4-chola-ene-24-oic acidethyl ester

3-oxo-4,6-choladien-24-oic acid ethyl ester (1.37 g, 4.27 mmol) wascharged to a reaction vessel, followed by BHT (23 mg, 0.13 mmol), EtOAc(11 mL) and water (3.4 mL) with stirring. The solution was heated to 80°C. and then a solution of mCPBA 70% (1.5 g, 7.51 mmol) in EtOAc (7.5 mL)was added dropwise over 15 mins. The reaction mixture was stirred at 70°C. for 2 h (IPC by TLC, 3:7 EtOAc:Heptane; visualized with Anisaldehydestain), cooled to ambient temperature and then washed with 1M aq.NaOH(2×20 mL) followed by 10% aq. NaS₂O₃: 2% NaHCO₃ (3×20 mL). The organicphases were dried over Na₂SO₄ and concentrated in vacuo at 40° C. Thecrude solids were crystalized from EtOAc (3 vol) at 60° C. to give anoff white solid which was dried under vacuum at 40° C. to give (6α,7α)-6,7-epoxy-3-oxo-4-chola-ene-24-oic acid ethyl ester (0.90 g).

Example 13—Synthesis of (6β,7α)-6-ethyl-7-hydroxy-3-oxo-4-cholen-24-oicacid ethyl ester

ZnCl₂ (600 mg, 4.25 mmol) was charged to a reaction vessel and driedunder vacuum at 180° C. for 1 h. The reaction vessel was cooled toambient temperature, THF (15 mL) charged and the contents of thereaction vessel cooled to 3° C. A solution of 3M EtMgBr in Et₂O (1.5 mL,4.25 mmol) was charged to the reaction vessel over 40 mins maintainingthe temperature below 5° C. The reaction mixture was then stirred for 1h. (6α, 7α)-6,7-epoxy-3-oxo-4-chola-ene-24-oic acid ethyl ester (0.80 g,1.93 mmol) in THF (6 mL) was charged to the reaction vessel over 40mins, maintaining the temperature below 5° C. CuCl (20 mg, 0.19 mmol)was charged in one portion and the reaction stirred at ambienttemperature for 16 h (IPC by TLC, 3:7 EtOAc:Heptane; visualized withAnisaldehyde stain). The reaction mixture was cooled in an ice bath andsat. aq.NH₄Cl was added dropwise, maintaining the temperature below 10°C. The reaction mixture was filtered and the filter cake washed withTBME (12.5 vol). The organic phase of the filtrate was separated and theaqueous phase extracted with TBME (2×12.5 vol). The combined organicphases were washed with 5% NaCl (3×12.5 vol) and concentrated in vacuoat 40° C.

Example 14—Synthesis of (6β, 5β,7α)-6-ethyl-7-hydroxy-3-oxo-cholan-24-oic acid ethyl ester

10% Pd/C (70 mg) was charged to a reaction vessel under an argonatmosphere followed by the crude material from Example 13 in DMF (14.6mL). The mixture was cooled to −10° C. and the reaction vessel wasevacuated then filled with hydrogen three times with vigorous stirring.The mixture was stirred under an atmosphere of hydrogen for 24 h whilemaintaining the temperature at −10° C. (IPC by TLC, eluent 1:1EtOAc:Heptane; visualized with Anisaldehyde stain) then the flask wasevacuated, filled with argon and filtered through a pad of celite andrinsed with DMF (7 mL). 10% Pd/C (70 mg) was recharged to the reactionvessel under an argon atmosphere followed by the DMF reaction mixture.The mixture was cooled to approximately −10° C. and the reaction vesselwas evacuated then filled with hydrogen three times with vigorousstirring. The mixture was stirred under an atmosphere of hydrogen for 24h at −10° C. (IPC by TLC, 1:1 EtOAc:Heptane; visualized withAnisaldehyde stain) then the flask was evacuated, filled with argon andfiltered through a pad of celite and washed with TBME (62.5 vol, 50 mL).The filtrate was washed with 10% aq. NaCl (4×25 vol), dried over Na₂SO₄,filtered and concentrated in vacuo at 40° C. Purification by columnchromatography (SiO₂, 0-30% Heptane:EtOAc) gave (6β, 5β,7α)-6-ethyl-7-hydroxy-3-oxo-cholan-24-oic acid ethyl ester (0.17 g). Theproduct was identical to the material obtained from plant origin (6β,7α, 22E)-6-ethyl-7-hydroxy-3-oxo-4,22-choladien-24-oic acid ethyl ester(see Example 4).

Examples 15 to 17 Conversion of (6β5β,7α)-6-ethyl-7-hydroxy-3-oxo-cholan-24-oic acid ethyl ester to (3α, 5β,6α, 7α)-6-ethyl-3,7-dihydroxy-cholan-24-oic acid Example 15—Synthesis of(6β, 5β)-3,7-dioxo-6-ethyl-cholan-24-oic acid ethyl ester

Method 1

A solution of Jones's reagent prepared from CrO₃ (1.10 g, 11 mmol) inH₂SO₄ (1.4 mL) and made to 5 mL with water was charged dropwise to asolution of (6β, 5β, 7α)-6-ethyl-7-hydroxy-3-oxo-cholan-24-oic acidethyl ester (0.18 g, 0.40 mmol) in acetone (10 mL) until an orangecolour persisted. The reaction mixture was quenched with IPA (1 mL),filtered through a 0.45 μm nylon syringe filter and the filter waswashed with acetone (10 mL). The combined filtrate and wash wasconcentrated, the residue was dissolved in EtOAc (20 mL) and washed withwater (2×10 mL). The aqueous phase was extracted with EtOAc (20 mL), thecombined EtOAc phases were concentrated and the residue was dissolvedand concentrated from toluene (20 mL) then acetone (20 mL) to give aclear oil containing (6β, 5β,7α)-6-ethyl-7-hydroxy-3,7-dioxo-cholan-24-oic acid ethyl ester (185 mg).

¹H NMR (700 MHz, CDCl₃): δ=4.12 (2H, q, J=7.1), 2.42 (1H, t, J=11.4),2.38-2.17 (6H, m), 2.09-1.74 (9H, m), 1.68-1.11 (17H, m), 0.93 (3H, d,J=6.5), 0.85 (3H, t, J=7.4), 0.72 (3H, s). ¹³C NMR (100 MHz, CDCl₃):δ=214.5, 211.4, 174.0, 60.1, 57.1, 55.1, 50.3, 48.4, 47.3, 44.9, 43.6,43.1, 39.2, 35.8, 35.2 (×2), 34.9, 31.3, 30.9, 28.1, 24.6, 23.7, 23.4,21.7, 18.3, 14.2, 12.6, 12.2. (IR) v_(max)(cm⁻¹): 2950, 2872, 1709,1461, 1377, 1304, 1250, 1177, 1097, 1034; HRMS (ESI-TOF) m/z: (M+H)⁺calcd for C₂₈H₄₅O₄ 445.3318; found: 445.3312;

Method 2

To a solution of (6β, 5β, 7α)-6-ethyl-7-hydroxy-3-oxo-cholan-24-oic acidethyl ester (41.0 g crude mass) in anhydrous CH₂Cl₂ (600 mL) at 0° C.was added solid DMP (34.0 g, 80.2 mmol) portion-wise over 20 mins(exothermic). The mixture was stirred at 0-5° C. for 2 h, then a furtherportion of DMP (4.0 g, 9.4 mmol) was added and reaction stirred at 0-5°C. for 1 h. The mixture was filtered through a GFA filter and the solidrinsed with CH₂Cl₂ (50 mL), the filtrate was stirred vigorously with 10%aq. Na₂S₂O₃ and 2% aq. NaHCO₃ (100 mL) for 20 mins. The phases wereseparated and the aq. extracted with CH₂Cl₂ (2×100 mL). The combinedorganic extracts were washed with 1M NaOH (100 mL). The mixture wasdiluted with CH₂Cl₂ (300 mL) and phases separated. The organic layer wasconcentrated under reduced pressure and the residue (cloudy brown oil)was dissolved in TBME (600 mL) and washed with 1M NaOH (100 mL) and NaCl(3×100 mL). The organic phase was concentrated in vacuo to give a darkyellow runny oil, crude mass 38.1 g. The oil was dissolved in EtOH (400mL) and stirred with activated charcoal (10 g) at 50° C., the mixturewas then filtered, the charcoal rinsed with EtOH (200 mL) and thefiltrate concentrated in vacuo to give (6β,5β)-3,7-dioxo-6-ethyl-cholan-24-oic acid ethyl ester as a yellow oil(35.9 g).

Method 3

A solution of (6β, 5β, 7α)-6-ethyl-7-hydroxy-3-oxo-cholan-24-oic acidethyl ester (218 mmol) in DMF (450 ml), CH₃CN (540 mL) and H₂O (90 mL)was charged into a 2 L vessel and cooled to 9° C., then AcOH (180 mL)was charged, followed by NaBr (4.1 g). A solution of sodium hypochlorite(˜10.5% w/v, 450 mL) was added dropwise over 1.5 h, maintaining theinternal temperature at 5-6° C., then the mixture was stirred for 5 h at7° C. TLC of the reaction mixture indicated complete consumption of thestarting material (IPC by TLC, eluent EtOAc/heptane 3:7, Rf for (6β, 5β,7α)-6-ethyl-7-hydroxy-3-oxo-cholan-24-oic acid ethyl ester=0.34; (6β,5β)-3,7-dioxo-6-ethyl-cholan-24-oic acid ethyl ester=0.45). A solutionof aq. 10% w/v Na₂SO₃ (360 mL) was charged dropwise with vigorousstirring, maintaining the internal temperature at 8-10° C., then H₂O(270 mL) was added dropwise and the mixture stirred at 5° C. for 16 h.The solid was filtered and washed with H₂O (720 mL). The solid was thendissolved in TBME (1.1 L) and subsequently washed with an aq. NaHCO₃(300 mL) and 10% brine (300 mL). The organic phase was then stirred withactivated charcoal (10 g) for 20 mins at 40° C., treated with anhydrousMgSO₄ (5 g) and filtered via GFA filter paper, the filter cake wasrinsed with TBME (50 mL) and the filtrate concentrated in vacuo to give(6β, 5β)-3,7-dioxo-6-ethyl-cholan-24-oic acid ethyl ester as light brownoil which solidifies on standing (82.7 g).

Example 16—Synthesis of (6α, 5β)-3,7-dioxo-6-ethyl-cholan-24-oic acid

Into a 500 mL flask was charged 0.5 vol of 0.5 M NaOH (9 mL) followed by(6β, 5β)-3,7-dioxo-6-ethyl-cholan-24-oic acid ethyl ester from Example15 (18.00 g, 1 eq) and then IPA (180 mL, 10 vol) (the initial NaOHcharge was to avoid the possibility of C3-ketal formation). The mixturewas warmed to 60±2° C. and held until a solution was obtained (10-15mins). The remaining 0.5 M NaOH solution (171 mL, 9.5 vol) was chargedover 20 mins and then the reaction was stirred for a further 3.5 h at60±2° C. The IPA was removed under vacuum at 60° C. and then 2M HCl (8mL) charged to pH 9. EtOAc was charged (90 mL, 5 vol) followed by 2M HCl(54 mL) to pH 1. Vigorous mixing was followed by phase separation. Theaqueous phase was back extracted with additional EtOAc (90 mL, 5 vol)and then the combined organic phases were washed with water (54 mL, 3vol), followed by three portions of 10% aq. NaCl (3×54 mL, 3×3 vol). Theorganic phase was treated with activated charcoal (100 mesh powder, 3.37g, ˜0.20 mass eq) for 12 mins and then filtered through GF/B.Concentration at 50° C. in vacuo gave (6α,5β)-3,7-dioxo-6-ethyl-cholan-24-oic acid (FIG. 2) as a light yellow foamin quantitative yield.

¹H NMR (700 MHz, CDCl₃): δ=2.74 (1H, dd, J=12.8, 5.4), 2.47 (1H, t,J=12.5), 2.43-0.90 (32H, m), 0.81 (3H, t, J=7.4), 0.70 (3H, s). ¹³C NMR(100 MHz, CDCl₃): δ=212.1, 210.6, 179.4, 54.9, 52.4, 52.3, 50.0, 48.9,43.7, 42.7, 38.9, 38.3, 36.7, 36.0, 35.5, 35.2, 30.9, 30.7, 28.2, 24.6,22.9, 22.3, 18.6, 18.3, 12.1, 11.8. (IR) v_(max)(cm⁻¹): 2939, 2873,1706, 1458, 1382, 1284.8. HRMS (ESI-TOF) m/z: (M+H)⁺ calcd for C₂₆H₄₁O₄417.3005; found: 417.2997; mp=71.2-75.9° C.

Example 17—Synthesis of (3α, 5β, 6α,7α)-6-ethyl-3,7-dihydroxy-cholan-24-oic acid

To a solution of crude (6α, 5β)-6-ethyl-3,7-dioxo-cholan-24-oic acid(21.7 g crude mass) in H₂O (260 mL) and 50% NaOH (15.2 mL) at 90° C. wasadded, dropwise, a solution of NaBH₄ (4.4 g, 116.3 mmol) in aq. NaOH(prepared from 25 mL of H₂O and 0.8 mL 50% NaOH). The mixture was heatedto reflux and stirred for 3 h. The mixture was then cooled to 60° C. anda 2M solution of HCl (200 mL) added dropwise with vigorous stirring.nBuOAc (100 mL) was then charged to the reaction flask and the mixturestirred for a further 20 mins. The phases were separated and the aqueousphase (pH=½) extracted with nBuOAc (100 mL). The combined organic phaseswere washed with 2M HCl (50 mL) and 10% aq. NaCl (100 mL). The organicsolvent was distilled off under reduced pressure at 70-80° C. Theresidue (dense oil) was dissolved in nBuOAc (60 mL) at 70° C. andallowed to gradually cool to room temperature, then stored at 6° C. for2 h. The solid was collected via filtration, rinsed with cold nBuOAc (20mL), then dried under vacuum at 70° C. for 5 h to give (3α, 5β, 6α,7α)-6-ethyl-3,7-dihydroxy-cholan-24-oic acid as a white solid (8.2 g).

The invention claimed is:
 1. A process for the preparation of a compoundof general formula (I):

wherein: R¹ is C₁₋₄ alkyl optionally substituted with one or moresubstituents selected from halo, OR⁶ or NR⁶R⁷; where each of R⁶ and R⁷is independently selected from H or C₁₋₄ alkyl; R² is H, halo or OH or aprotected OH, which is stable under basic conditions; Y¹ is a bond or analkylene linker group having from 1 to 20 carbon atoms and optionallysubstituted with one or more R³ groups; each R³ is independently halo,OR⁸ or NR⁸R⁹; where each of R⁸ and R⁹ is independently selected from Hor C₁₋₄ alkyl; and R⁴ is C(O)OR¹⁰, OC(O)R¹⁰, C(O)NR¹⁰R¹¹, OR¹⁰,OSi(R¹³)₃), S(O)R¹⁰, SO₂R¹⁰, OSO₂R¹⁰, SO₃R¹⁰, or OSO₃R¹⁰; where each R¹⁰and R¹¹ is independently: a. hydrogen or b. C₁₋₂₀ alkyl, C₂₋₂₀ alkenyl,C₂₋₂₀ alkynyl, —O—C₁₋₂₀ alkyl, —O—C₂₋₂₀ alkenyl or —O—C₂₋₂₀ alkynyl, anyof which is optionally substituted with one or more substituentsselected from halo, NO₂, CN, OR¹⁹, SR¹⁹, SO₂R¹⁹, SO₃R¹⁹ or N(R¹⁹)₂, or a6- to 14-membered aryl or 5 to 14-membered heteroaryl group, either ofwhich is optionally substituted with C₁₋₆ alkyl, C₁₋₆ haloalkyl, halo,NO₂, CN, OR¹⁹, SR¹⁹, SO₂R¹⁹, SO₃R¹⁹ or N(R¹⁹)2; or c. a 6- to14-membered aryl or 5 to 14-membered heteroaryl group optionallysubstituted with one or more substituents selected from C₁₋₆ alkyl, C₁₋₆haloalkyl, halo, NO₂, CN, OR¹⁹, SR¹⁹, SO₂R¹⁹, SO₃R¹⁹ or N(R¹⁹)₂; d. apolyethylene glycol residue; each R¹⁹ is independently selected from H,C₁₋₆ alkyl, C₁₋₆ haloalkyl, or a 6- to 14-membered aryl or 5 to14-membered heteroaryl group optionally substituted with halo, C₁₋₆alkyl or C₁₋₆ haloalkyl; each R¹³ is independently a. C₁₋₂₀ alkyl, C₂₋₂₀alkenyl or C₂₋₂₀ alkynyl optionally substituted with one or moresubstituents selected from halo, NO₂, CN, OR¹⁹, SR¹⁹, SO₂R¹⁹, SO₃R¹⁹ orN(R¹⁹)₂, a 6- to 14-membered aryl or 5 to 14-membered heteroaryl group,either of which is optionally substituted with C₁₋₆ alkyl, C₁₋₆haloalkyl, halo, NO₂, CN, OR¹⁹, SO₂R¹⁹, SO₃R¹⁹ or N(R¹⁹)₂; or b. a 6- to14-membered aryl or 5 to 14-membered heteroaryl group optionallysubstituted with one or more substituents selected from C₁₋₆ alkyl, C₁₋₆haloalkyl, halo, NO₂, CN, OR¹⁹, SR¹⁹, SO₂R¹⁹, SO₃R¹⁹ or N(R¹⁹)₂; eachR¹⁹ is independently selected from H, C₁₋₆ alkyl or C₁₋₆ haloalkyl;R^(5b) is H or OH or a protected OH; or a salt thereof comprising: A.epimerization of a compound of general formula (II):

wherein Y¹, R¹, R², and R⁴ are of general formula (I) and R⁵ is H or OHor a protected OH; by treatment with a base; or B. conversion of acompound of general formula (I) in which R⁴ is C(O)OR¹⁰ to anothercompound of general formula (I) by a process comprising: i. for acompound of general formula (I) in which R⁴ is OSO₃R¹⁰: reacting acompound of general formula (I) in which R⁴ is C(O)OR¹⁰ with a reducingagent followed by reaction with chlorosulfuric acid in the presence of abase; ii. for a compound of general formula (I) in which R⁴ is OSO₂R¹⁰:reacting a compound of general formula (I) in which R⁴ is C(O)OR¹⁰ witha reducing agent followed by reaction with chlorosulfurous acid; iii.for a compound of general formula (I) in which R⁴ is C(O)NR¹⁰R¹¹:reacting a compound of general formula (I) in which R⁴ is C(O)OH with anamine of formula H—NR¹⁰R¹¹.
 2. A process according to claim 1 wherein,in the compound of general formula (I), R¹ is ethyl.
 3. A processaccording to claim 1 wherein, in the compound of general formula (I), Y¹is an alkylene linker group having from 1 to 8 carbon atoms andoptionally substituted with one or more R³ groups.
 4. A processaccording to claim 1 wherein, in the compound of general formula (I),independently or in any combination: Y¹ is a bond or an alkylene grouphaving 1 to 3 carbon atoms and is optionally substituted with one or twoR³ groups; R⁴ is C(O)OR¹⁰, SO₃R¹⁰, or OSO₃R¹⁰, where R¹⁰ is selectedfrom H, C₁₋₆ alkyl or benzyl; R^(5b) is H or OH.
 5. A process accordingto claim 4 wherein, in the compound of general formula (I),independently or in any combination: R¹ is ethyl; and/or R² is H; and/orY¹ is a bond, —CH₂— or —CH₂CH₂—; and/or R⁴ is C(O)OR¹⁰, where R¹⁰ is H,C₁₋₆ alkyl or benzyl; and/or R^(5b) is H.
 6. A process according toclaim 1 wherein the compound of general formula (I) is selected from thegroup consisting of (6β, 5β)-3,7-dioxo-6-ethyl-cholan-24-oic acid andC₁₋₆ alkyl and benzyl esters thereof and salts thereof.
 7. A processaccording to claim 1 wherein, in the compound of general formula (II),R⁴ is C(O)OR¹⁰, where R¹⁰ is C₁₋₆ alkyl or benzyl, wherein the base is astrong base, wherein the strong base is selected from sodium orpotassium hydroxide, and where epimerization is accompanied byhydrolysis to give a compound of general formula (I) in which R⁴ isC(O)OH.
 8. A process according to claim 1 wherein, in the compound ofgeneral formula (II), R² and/or R⁵ is a protected OH which is stable inbasic conditions and the process optionally comprises and additionalstep of removing the protecting group to give a compound of generalformula (I) in which R² and/or R^(5b) is OH.
 9. A process according toclaim 1 for the preparation of a compound of general formula (I) inwhich R⁴ is C(O)OR¹⁰.
 10. A process for the preparation of a compound ofgeneral formula (XXI):

wherein: R¹ is C₁₋₄ alkyl optionally substituted with one or moresubstituents selected from halo, OR⁶ or NR⁶R⁷; where each of R⁶ and R⁷is independently selected from H or C₁₋₄ alkyl; Y¹ is a bond or analkylene linker group having from 1 to 20 carbon atoms and optionallysubstituted with one or more R³ groups; each R³ is independently halo,OR⁸ or NR⁸R⁹; where each of R⁸ and R⁹ is independently selected from Hor 014 alkyl; and R⁴ is C(O)OR¹⁰, OC(O)R¹⁰, C(O)NR¹⁰R¹¹, OR¹⁰,OSi(R¹³)₃) S(O)R¹⁰, SO₂R¹⁰, OSO₂R¹⁰, SO₃R¹⁰, or OSO₃R¹⁰; where each R¹⁰and R¹¹ is independently: a. hydrogen or b. C₁₋₂₀ alkyl, C₂₋₂₀ alkenyl,C₂₋₂₀ alkynyl, —O—C₁₋₂₀ alkyl, —O—C₂₋₂₀ alkenyl or —O—C₂₋₂₀ alkynyl, anyof which is optionally substituted with one or more substituentsselected from halo, NO₂, CN, OR¹⁹, SR¹⁹, SO₂R¹⁹, SO₃R¹⁹ or N(R¹⁹)₂, or a6- to 14-membered aryl or 5 to 14-membered heteroaryl group, either ofwhich is optionally substituted with C₁₋₆ alkyl, C₁₋₆ haloalkyl, halo,NO₂, CN, OR¹⁹, SR¹⁹, SO₂R¹⁹, SO₃R¹⁹ or N(R¹⁹)2; or c. a 6- to14-membered aryl or 5 to 14-membered heteroaryl group optionallysubstituted with one or more substituents selected from C₁₋₆ alkyl, C₁₋₆haloalkyl, halo, NO₂, CN, OR¹⁹, SR¹⁹, SO₂R¹⁹, SO₃R¹⁹ or N(R¹⁹)₂; d. apolyethylene glycol residue; each R¹⁹ is independently selected from H,C₁₋₆ alkyl, C₁₋₆ haloalkyl, or a 6- to 14-membered aryl or 5 to14-membered heteroaryl group optionally substituted with halo, C₁₋₆alkyl or C₁₋₆ haloalkyl; each R¹³ is independently a. C₁₋₂₀ alkyl, C₂₋₂₀alkenyl or C₂₋₂₀ alkynyl optionally substituted with one or moresubstituents selected from halo, NO₂, CN, OR¹⁹, SR¹⁹, SO₂R¹⁹, SO₃R¹⁹ orN(R¹⁹)₂, a 6- to 14-membered aryl or 5 to 14-membered heteroaryl group,either of which is optionally substituted with C₁₋₆ alkyl, C₁₋₆haloalkyl, halo, NO₂, CN, OR¹⁹, SO₂R¹⁹, SO₃R¹⁹ or N(R¹⁹)₂; or b. a 6- to14-membered aryl or 5 to 14-membered heteroaryl group optionallysubstituted with one or more substituents selected from C₁₋₆ alkyl, C₁₋₆haloalkyl, halo, NO₂, CN, OR¹⁹, SR¹⁹, SO₂R¹⁹, SO₃R¹⁹ or N(R¹⁹)₂; eachR¹⁹ is independently selected from H, C₁₋₆ alkyl or C₁₋₆ haloalkyl; R²is H, halo or OH; and R^(5a) is H or OH; the process comprising: i.reduction of a compound of general formula (I):

wherein: R¹ is C₁₋₄ alkyl optionally substituted with one or moresubstituents selected from halo, OR⁶ or NR⁶R⁷; where each of R⁶ and R⁷is independently selected from H or C₁₋₄ alkyl; R² is H, halo or OH or aprotected OH, which is stable under basic conditions; Y¹ is a bond or analkylene linker group having from 1 to 20 carbon atoms and optionallysubstituted with one or more R³ groups; each R³ is independently halo,OR⁸ or NR⁸R⁹; where each of R⁸ and R⁹ is independently selected from Hor C₁₋₄ alkyl; and R⁴ is C(O)OR¹⁰, OC(O)R¹⁰, C(O)NR¹⁰R¹¹, OR¹⁰,OSi(R¹³)₃, S(O)R¹⁰, SO₂R¹⁰, OSO₂R¹⁰, SO₃R¹⁰, or OSO₃R¹⁰; where each R¹⁰and R¹¹ is independently: a. hydrogen or b. C₁₋₂₀ alkyl, C₂₋₂₀ alkenyl,C₂₋₂₀ alkynyl, —O—C₁₋₂₀ alkyl, —O—C₂₋₂₀ alkenyl or —O—C₂₋₂₀ alkynyl, anyof which is optionally substituted with one or more substituentsselected from halo, NO₂, CN, OR¹⁹, SR¹⁹, SO₂R¹⁹, SO₃R¹⁹ or N(R¹⁹)₂, or a6- to 14-membered aryl or 5 to 14-membered heteroaryl group, either ofwhich is optionally substituted with C₁₋₆ alkyl, C₁₋₆ haloalkyl, halo,NO₂, CN, OR¹⁹, SR¹⁹, SO₂R¹⁹, SO₃R¹⁹ or N(R¹⁹)2; or c. a 6- to14-membered aryl or 5 to 14-membered heteroaryl group optionallysubstituted with one or more substituents selected from C₁₋₆ alkyl,C₁₋₆haloalkyl, halo, NO₂, CN, OR¹⁹, SR¹⁹, SO₂R¹⁹, SO₃R¹⁹ or N(R¹⁹)₂; d.a polyethylene glycol residue; each R¹⁹ is independently selected fromH, C₁₋₆ alkyl, C₁₋₆ haloalkyl, or a 6- to 14-membered aryl or 5 to14-membered heteroaryl group optionally substituted with halo, C₁₋₆alkyl or C₁₋₆ haloalkyl; each R¹³ is independently a. C₁₋₂₀ alkyl, C₂₋₂₀alkenyl or C₂₋₂₀ alkynyl optionally substituted with one or moresubstituents selected from halo, NO₂, CN, OR¹⁹, SR¹⁹, SO₂R¹⁹, SO₃R¹⁹ orN(R¹⁹)₂, a 6- to 14-membered aryl or 5 to 14-membered heteroaryl group,either of which is optionally substituted with C₁₋₆alkyl, C₁₋₆haloalkyl, halo, NO₂, CN, OR¹⁹, SO₂R¹⁹, SO₃R¹⁹ or N(R¹⁹)₂; or b. a 6- to14-membered aryl or 5 to 14-membered heteroaryl group optionallysubstituted with one or more substituents selected from C₁₋₆ alkyl,C₁₋₆haloalkyl, halo, NO₂, CN, OR¹⁹, SR¹⁹, SO₂R¹⁹, SO₃R¹⁹ or N(R¹⁹)₂;each R¹⁹ is independently selected from H, C₁₋₆ alkyl or C₁₋₆ haloalkyl;R^(5b) is H or OH or a protected OH; or a salt thereof using a reducingagent and, where R² and/or R^(5b) is a protected OH, removal of theprotecting group(s), to give the compound of general formula (XXI),wherein removal of the protecting group can take place before or afterthe reduction; and optionally ii. conversion of a compound of generalformula (XXI) in which R⁴ is C(O)OR¹⁰ to another compound of generalformula (XXI) by a process comprising: i. for a compound of generalformula (XXI) in which R⁴ is OSO₃R¹⁰: reacting compound of generalformula (XXI) in which R⁴ is C(O)OR¹⁰ with a reducing agent followed byreaction with chlorosulfuric acid in the presence of a base; ii. for acompound of general formula (XXI) in which R⁴ is OSO₂R¹⁰: reacting acompound of general formula (XXI) in which R⁴ is C(O)OR¹⁰ with areducing agent followed by reaction with chlorosulfurous acid; iii. fora compound of general formula (XXI) in which R⁴ is C(O)NR¹⁰R¹¹: reactinga compound of general formula (XX) in which R⁴ is C(O)OH with an amineof formula H—NR¹⁰R¹¹.
 11. A process according to claim 10 wherein thereducing agent is a hydride.
 12. A process according to claim 10 for thepreparation of a compound of formula (XXI) in which R¹ is ethyl, R² andRya are both H, Y¹ is —CH₂CH₂—, and R⁴ is C(O)OH.